https://www.flamingolasvegas.com/Mak...=OGY0000319323
Follow that link, promo code PFSTL. You can get Flamingo standard rooms (nice, clean) for $35/night during the week or the new renovated GO rooms for a little more. The GO rooms are really sweet with a plasma screen TV and even a TV in the bathroom mirror that appears when you turn it on. The Flamingo is also in a prime location. It's next door to the Imperial Palace that someone mentioned earlier, but the Imperial Palace is pretty crusty.
Definitely go to the VooDoo lounge at the Rio. It's an outside rooftop club that overlooks the entire strip. It's the one thing I'd say you really don't want to miss.
Also, I'm not sure of your age, but most of the hotels now have "day clubs" at their swimming pools with music, dancing, and some that allow topless sunbathing. It's really fun, but leave time for a nap. We got exhausted by getting drunk during the day and then trying to go out at night with no nap in between. It can be hard to balance the day partying and night partying.