As a local I vote for the buffet at Bellagio (especially good if somebody else is picking up the tab.), Aladdin and Paris. (Hint, at Paris the noon price doesn't change until about 5:30P.M. so get there at about 5:00 and they put out the King Crab at 5:30)
Several of the cheaper buffets have slipped a little and it's definately worth the extra to go to the best.
I like the Prime Rib special in the coffee shop at the California.
I second the Mexican Restaurant at the Suncoast.