Tao Beach!!!If you're into house (I am), I would recommend the following:
1. Hakkasan @ MGM in the evenings - recommend getting a booth, pricey but worth it
2. Marquee @ Cosmopolitan (day/ pool club) - no need for a cabana
3. Wet Republic @ MGM (day/ pool club) - recommend getting a cabana
4. Tao Beach @ The Venetian - recommend getting a booth
There are several other's, but these are fun, upscale and chill.