Hi! A Thai guy here. I haven't watched many of the lakorns everyone mentioned because I watch Korean dramas more, but I'll suggest the hidden gems that Thai people like very much and others don't really know of!

ผู้กองยอดรัก Phu Khong Yod Rak / Poo Kong Yod Rak --
this is a romantic comedy that has been remade many times.
The latest version from 2015 should have subtitles, I think. It's really good!!!!
http://mydramalist.com/19454-phu-khong-yod-rak (2001) -- most beautiful lead actress
http://mydramalist.com/15760-phu-khong-yod-rak (2015) -- funniest male lead
http://mydramalist.com/19452-poo-kong-yod-rak (2006) -- don't remember this one lol

นาคี Narkee --
at least it was SUPER POPULAR in Thailand last year.
It's set in modern time but it has historical elements because lead lady
has a lot in connection with a goddess from the past.
If you like Ken Phupoom then watch it!
It started airing before the late King Bhumibhol of Thailand passed away last year
so the airing of all dramas was stopped, but after a while they started airing again
and this one was the only drama that started airing from the first episode
because people requested it so much.
http://mydramalist.com/18908-narkee

ตามรักคืนใจ Tarm Ruk Keun Jai --
This one has Nadech in it. It's set in beautiful Northern region of Thailand.
He has a lot of action scenes in here but it's not completely an action drama.
The sweetheart of viewers was Naram (Au Tanakorn) who is probably
more charismatic and handsome than Nadech LOL!
http://mydramalist.com/11436-tarm-ruk-keun-jai

ดาวเกี้ยวเดือน Dao Kiao Duen --
The leads are hot and the male lead's younger sister is also hot
and she's also a very lovable character. She rocks actually!
Really good lakorn and Janie was so pretty in here.
You just gotta watch it. Don't mind her annoyingly overprotective older bro.
http://mydramalist.com/9956-dao-kiao-duen

ดาวเคียงเดือน Dao Kiang Duen --
This is the spinoff of that previous one above.
I haven't seen this one but the reaction in Thailand was really good as well.
Some says that this story is better than it's parent story.
I don't know. I should watch it soon. 
http://mydramalist.com/10731-dao-kiang-duen

แรงเงา Raeng Ngao --
I seem to keep recommending Ken Phupoom's drama LOL
He's not even my favorite but he picks all the good dramas.
This one has Janie too. She plays two roles and her performance was EXTRAORDINARY!
If you like strong female lead with some good slap skills, this is it.
She's smart, strong, beautiful, but I don't remember Ken's character.
http://mydramalist.com/10002-raeng-ngao
There's also second season coming soon http://mydramalist.com/24007-raeng-ngao-2

The Rising Sun Series --
รอยรักหักเหลี่ยมตะวัน Roy Ruk Hak Liam Tawan (watch this first)
http://mydramalist.com/10503-roy-ruk-hak-liam-tawa...
รอยฝันตะวันเดือด Roy Fun Tawan Duerd
http://mydramalist.com/10344-roy-fun-tawan-duerd
The series is set in Japan and features some samurai actions (LOL)
and they have the best leads, Nadech & Yaya, Mario & Taew!
There's also Golf Pichaya (Mike D'Angelo's brother)
and the hot Au Tanatorn from my third recommendation above.
If you don't mind some weird logic like how they speak Thai in this "Japanese" drama
then watch it. It's good and beautiful to look at.

หยกลายเมฆ Yok Lai Mek (Cloud Jade) --
This one is old and it was really famous in Thailand.
This is also a revenge story where the romance is a bit weak (but there is a main couple)
The comments on this page doesn't look good. Why?
I remember liking this one a lot. Janie is in here again.
A lot of shooting was done in Hong Kong.
They have good villain(s) in here. Amazing acting by everyone but main guy LOL.
http://mydramalist.com/10286-yok-lai-mek

(insert epic music)
คู่กรรม Koo Gum --
THIS IS HUGE. THIS IS A MUST WATCH.
This was based on a bestselling novel from looooong ago
and the drama has been produced multiple times.
I think the latest version should have subtitles and it was a good remake too.
This is story about Japanese soldier and Thai woman during World War II.
It's a tragic love story with war background with amazing soundtrack.
Choose the version you like:
http://mydramalist.com/10316-koo-gum-2013 (drama 2013) RECOMMEND!
http://mydramalist.com/10098-koo-gum-movie-2013 (movie 2013 with Nadech) REC!
http://mydramalist.com/10405-koo-gum-2004 (drama 2003 or 2004 - most popular in Thailand) REC!
http://mydramalist.com/10406-koo-gum (too old I wasn't born yet LOL)
http://mydramalist.com/15361-koo-gum
(even older but I wanna watch this, it has Warut Woratam as lead - he's good!!!)
http://mydramalist.com/20644-sunset-at-chaophraya (also old movie that I haven't seen)
(THE song https://www.youtube.com/watch?v=pR4IdyCmglE)

คิวบิก Cubic --
I hate to recommend this one because I hated how this one
was a BIG disgrace to its original novel. 
Still, check it out. Read my comment on that drama page.
The base story is actually VERY well planned out.
Very good action featuring strong female lead.
http://mydramalist.com/9938-cubic

สุภาพบุรุษจุฑาเทพ The Gentlemen of Jutathep Series --
This was popular for featuring up-and-coming male leads.
I suggest girls to watch this for the guys,
but I'm a guy and I'm not very fond of any of these lead girls.
Story could be typical but the production was huge so give it a try.
1. http://mydramalist.com/10020-khun-chai-taratorn
2. http://mydramalist.com/10024-khun-chai-pawornruj
3. http://mydramalist.com/10062-khun-chai-puttipat
4. http://mydramalist.com/10065-khun-chai-rachanon
5.http://mydramalist.com/10088-khun-chai-ronapee
I recommend part 5 because both leads are good.

Many people suggested these and I agree:
http://mydramalist.com/16323-padiwaradda
http://mydramalist.com/13865-kleun-cheewit
http://mydramalist.com/13397-leh-ratree
Right now this one is airing and it's good (quite K-drama like) 
http://mydramalist.com/20580-game-maya

I personally don't watch teen-targeted series like Hormones and Ugly Duckling etc.
Hope you enjoy those dramas. Hope they have subtitles!!!!


EDIT: also add this
ทวิภพ Tawipob --
It's historical and has time travel.
It's not sci-fi like other time travel dramas.
It's a good piece of romance and drama and historical.
Beautiful costumes and historical scenes.
http://mydramalist.com/9841-tawipob-2011

New to Lakorns but I have watched a few (mostly by GMM because they are so easy to find) I am a big fan of romance and comedy so most of the ones I have watched are that.

U-Prince Series
Kiss Me
Ugly Duckling Series
Secret Love Series
Full House
SOTUS

More of the slap/kiss variety but still really really good (and actually have some cute parts as well.)

Leh Ratree (2015 version w/ Sean and Esther)
Kleun Cheewit
ON the top of my list is 
1. full house: best romcom having all in 1 go... 
2. den second would be wanneung jaa pben superstar: again a romcom wid our very hottie push. n story of a girl who want to become a superstar.
3. kiss me thai..
4. roy leh sanae rai
5. leh nangfah
@Dapz

Where did you find Leh Nangfah? I have been wanting to watch that one^^
This thread has convinced me to check out thai dramas, thanks!

Now it's another language I need to get used to xD
Check out those videos:
Top 10 Thai dramas (lakorns) for beginners! (both comedy & slap/Kiss)
https://www.youtube.com/watch?v=SRkJAEFMWkU&t=2s
if you are specifically into Slap/Kiss genre then check those five dramas:
Top 5 Slap/Kiss thai dramas ( lakorns ) - NO RAPE!
https://www.youtube.com/watch?v=Wj2NUdFIspk
I hope that helped ^^
Where do people go to find Thai dramas? I have found that kissasian.com, fastdrama.co, and youtube (mostly GMM dramas) have Thai dramas, but does anyone know anywhere else? Like I know people have seen Lah Nengfah but I haven't been able to find it subbed TT
@OnigiriBunnie: You can find it on Dramacool with English Sub
Have only watched few lakorns but I highly recommend Kleun Cheewit (if and only if, as others may proclaim, if you're okay with very very light slap-kiss lakorns). It is literally one of the best dramas I've ever watched. 
@OnigiriBunnie: I am watching few Thai lakorns  H e r e with english subs :)
@moongchi and @royalmajesty thank you for the help  ^^
Below are my recommended thai drama list.

1. Cupid The Series
- In this series, they have 8 short mini dramas. My favourite series are Kammathep Prab Marn (Ken Teeradeth & Chompoo) & Kammathep Jum Laeng (Prang & Alek). Basically, the series is about how the employees of a matchmaking company, Cupid Hut find their soulmates/love.

2. Bride for Money/Jao Sao Rim Tang - Stefen & Poo. (Theme: Marriage of convinience)

3. The Husband/Samee (2013) - Grate & Pream

4. The One In My Heart/Neung Nai Suang (2005) - Ken Theeradeth & Janie. They also have the 2015 version, but I kinda like Ken as P'Neung compared to James Jirayuu.

5. Ruk Tong Om - Grate & Matt (About two friends taking care of an abandoned baby)

6. Suparburoot Jutathep Series - Khun Chai Taratorn (Grate & Pream)

7. Wiwa Wah Woon/Chaotic Marriage - Ken Teeradeth & Chompoo.

8. Kon Ruk Luang Jai - Ken Teeradeth & Janie
Kluen Cheewit-Yaya Urassaya Sperbund was just amazing, a strong female lead, she didn't have anyone to depend on but tries to help everyone, she is nice but strong...plus the story line was great, the characters were extra as normal but somehow didn't mind it that much. Her best friend and the nicer guys balanced out the annoying females.

https://alwaysmeena.wordpress.com i think it has everything about thai lakorn eng sub
My top list : 

1. SOTUS 
2. 2 moons the series
3. Project S the series
4. Water Boyy the series
5. U-Prince Single Lawyer