You can pay to get into the party pools like Wet Republic, Encore Beach club, Tao Beach and many others... The hotels usually also have a guest only pool and for those you need to be staying in the hotel because room key is required to access the pool (some of them will swipe the key to make sure that it's still active-Wynn & Bellagio do that, some you can just show the key to whoever is at the door). Sapphire Gentlemen's club  have a pool open on weekends (they call it Sapphire Day Club). I enjoy going there because you still get the party atmosphere, DJ, but it's rarely super crowded (and yes, guys. if you decide that you want a lap dance from one of their dancers that are attending the pool, the VIP room is open during that time).
As a true sun worshiper I love pool season but usually avoid going to the party ones on long weekends or big holidays as some of they get really overcrowded to the point that if you don't have a cabana, you barely have a place to stand. You might want to check out the night swim at Encore and some other pools this season. It's when the club has the pool open one of the evenings per week so you can party in club wear or have your swim suit underneath and take a dip in the water. I just love it!

I hope that this helps a bit and if you'd like to have an Exotic Brazilian accompanying you to the pool, check out my pool special at my website. I've heard that I look great in a bikini and even better out of it
Sweet Kisses...
Sofia