Been a while since I've been to Vegas, but my friend swears by the new Encore (the same hotel complex across from Wynn), mainly for the spa. Wynn is quite good too.
I loved the Bellagio, but as PP says, if you want to spend a bit for luxury, then go for it. I also liked Caesar's, the Venetian, Paris, Monte Carlo, and Luxor. Palms is great, but all I've been there for was the Ghost Bar, Rain, and the Lounge.
I've only got experience with TI and the Venetian on the strip, but both are right across from each other, pretty centrally located, and I liked both. I'll give the nod to TI (Treasure Island) due to their clubs and that they had a naked* asian chick on the door key, so that's where I stay when I go.
* - picture was taken from behind and showed the top of her crack to her neck, so mostly her back, but there were frontal curves on it as well. Nothing really, nothing I'd actually call "nudity", just found it interesting for that to be on the key card and thought I'd share.
Yes doctor, I am sick. Sick of those who are spineless. Sick of those who feel self-entitled. Sick of those who are hypocrites. Yes doctor, an army is forming. Yes doctor, there will be a war. Yes doctor, there will be blood.....