It really depends on what kind of atmosphere you want... Small and more intimate but a great party or a giant club. A good way to know where the best parties are is to find a few club promoters on facebook and you'll get all the deals and information on lists and everything. I have a few friends who work in club promotion, but I don't go out that often anymore. However, some of my favorites were:
Club Araoz: (1 block from araoz and Santa Fe) but it has a different name every night depending on the kind of party it's putting on. It's smaller and you're supposed to be 21+ for girls and 25+ for men to get in I think. but it's always a lot of fun!
Terrazas del Este: (Costanera Norte y Sarmiento) Now that it is getting warmer this place is going to be amazing! It's on the coast near Jorge Newberry and has a lot of outdoor dancing space. It's a beautiful club with a couple different dance floors, it's pretty big so you have your pick of different kinds of music usually.
Kika: (near plaza Serrano, Honduras 5339) I always have an amazing time in Kika! The next time I go out it will probably be here. It's maybe medium-sized with 2 dance floors but it is always packed and it is always a good party.
Caix: This place is really big and also on the coast with outdoor space and maybe 5 or 6 dance floors with different DJs if not more... It's a lot of fun, but I think the crowd is a little younger sometimes so it depends what you're looking for. I prefer to go here with a big crowd of friends to enjoy myself with them rather than meet people. Being female, I can say that the male crowd there tends to be pretty grabby which is why it's not my favorite, but if you're a guy and nice you might meet some great girls there who appreciate your manners...
Anyways, that's my short list of good places. If you have something specific in mind let me know and I'll try to tell you what fits your description.