I second the rec for Boss & Me if you're looking for a cute, relaxing Cinderella and the prince type romance.
Cruel Romance also falls into this category, but with a touch of danger thrown in to make things a bit more exciting.
Too Late to Say I Love You - a more mature romance with fairly good writing in terms of character development. For a C-drama, I was impressed because good writing seems to be an option in many romance C-dramas that I've seen. I loved it for the most part, but I always feel like I have to warn people about the ending in case you're a viewer who's big on endings. The last couple of episodes are not the best, but I still think it's worth a watch.
Loving, Never Forgetting - decent mixture of family drama, romance and corporate scheming. If you're a Jerry Yan fan, he's just delicious here ... as he always is. :)