They were romances or potential romances that were either brief, hinted at, mentioned but never seen, ended due to death or departure, or in some cases just seemed like they could have worked out in my head! Which couple do you think would have been awesome to see together for several episodes or seasons?
My vote is Jake & Ezri. I think it would have made things a little more interesting for Jake's character in the last season. Plus, it would have been funny to see Quark and Bashir (and perhaps Worf) drowining in their sorrows because the "boy" gets Dax in the end. And it would have been crazy for Ben Sisko to call his son's girlfriend "old man," and potentially create some tension between Ben & Ezri.
Second place for me would be Kira and Tom Riker. I thought they had great chemistry together and it would have been interesting to see him come back a few more times.
Third place for me is Kira & Damar. There wasn't much time for this to go anywhere (plus he was killed), but Damar was turning into a "new" Cardassian, and how crazy for Kira to go from someone who hates everything Cardassians stand for to falling in love with one.
Honorable mention to Jadzia and Boday just because I want to see the guy with the transparent skull!