If you're hanging out on the strip and feel the need to take a break and have a good beer, Pour 24 is always good. It's just a standalone bar in NYNY, but it has 24 taps of VERY good craft brews. When you walk over the bridge btw MGM Grand and NYNY, it's the first bar, straight ahead, as you enter NYNY. Next to Coyote Ugly.
If you wander off the strip, hit up Tanaya Creek Brewery. One of the brewers gave me a very homebrewer friendly tour there last April that was awesome. For selection of craft beer, the Pub in the Monte Carlo is good.