One of my fave themes!! If you want the girl friend-zoned, Ex-girlfriend club is perfect. It's a short, fun drama.
I suggest In Time With You (skip The Time We Were in Love) and Reply 1997 - guys friend-zoned, but they're great. They're meant to be and you just can't help rooting for them. Coincidentally, both have strong female leads and good male leads who support them. Best friends-turned-lovers dramas, IMO.