My girlfriend and I are doing 1 week in Bulgaria (sofia + petrich) this summer (around july 4th week) and we want to parlay that into a beach town somewhere in the balkans for about a week. So far, between the both of us we've done:
a) Black sea in Bulgaria
b) Croatia (split + dubrovnik)
c) Greek islands (santorini, milos, mykonos)

We're not totally opposed to other spots in southern europe, or even the ones above -- but I had some trouble coming up with things off the top of my head. What other recommendations do people have? I appreciate the responses!