well for starters you can check out the hard rock cafe
on the end of las ramblas..(the beginning begins at the harbor) next to the catalunya plaza..
it's just a bar and restaurant.. no dancing, but there is music and video monitors.. get there early to find a place at the bar it usually gets crowded after 8:00 pm..
most of the bars you'll find are on las ramblas street.
also there are tapas at just about every side street that connect las ramblas.. there's an australian bar that has a pretty good atmosphere, the bartender is from australia and americans seem to be welcomed there... also in catalunya plaza there is also an irish pub you can check out
if you like a classy bar you can try some of the local hotels on las ramblas.. don't remember the names but more quiet and cleaner..
if you are into dancing and the club scene you can try the sutton club.. in spain they pronounce it the "soo-tan-cloob"
lots of girls 20-30.. get there around 11:00 before the crowd..
as a tip i would stay away from the clubs at or near the beach..overcrowded and the bathrooms are filthy
the women in general are not forthcoming in meeting men, most women would rather be with their friends..
in my experience only a few women would come and talk with us but the vast majority were content being with their group..
anyway have fun and good luckwith your trip!