I'm not sure about episodes (I Read them more than watch) but two BIGGEST series that shouts Romance and some darker themes are.
Black Bird- Really good, I swear my friends and I were hooked on it for days. Highly reccomend.
Hadashi de bara wo fume- "Stepping on Roses" IT's not quite popular but it's still amazing and has a lot of darker/suggestive themes.
Others have already listed the ones I was thinking of. ^_^