Do you want mainstream hiphop? old school? indie? some soul or funk thrown in there?
As mentionned, Tokyo on Sundays - but I warn you the DJ is AWFUL, everytime I've been there the tracks are cut at awkward times, he cuts the music to let people sing for waaaay too long, he doesn't adjust his tempos correctly while mixing....it's just a big big mess in my opinion.
Otherwise (with more eclectic selection of hiphop/rap/rNb/etc than your simple radio playlist)-
Blizzarts on Tuesdays
Blue Dog on Sundays
Le Consulat either on Thursdays or Fridays (I forget and will let you take the time to look it up)
Velvet on Wednesdays
Other bars worth checking out Vinyl, Korova, Koï (don't particularly like the place - but may have what you're looking for musically), Muzique (though police ends up showing up every night for fights/gang problems), Academy, Gogo Lounge, Koko Lounge, and that's all that comes to mind right now. There are a bazillion other places downtown, but I'm not in that loop.