Pretty much my only reason to visit Vegas. One of the premiere multi-pitch trad climbing areas in the country, Red Rock NCA also has aid, sport and single pitch trad climbing routes, in addition to trails. The cliffs are sandstone, so you'll need to wait at least 24 after a rainstorm unless you want to content with potentially brittle holds. You can climb year round by chasing the shade/sun as appropriate. The newish campground is fairly dull, but slightly more convenient than the Strip purely in proximity to the climbing areas.
UPDATE (27 Apr 10)
Back to the 6a opening hours.
UPDATE (15 Jan 09)
The BLM is currently testing the feasibility of a 7am (v. 6am) opening time. The kiosk operators didn't know if this would be permanent. Also, a note about late exit permits for multi-pitch routes. Make sure that you include all of the requested information in your phone message or your permit will be rejected and you may be subject to a $125 fine. It's best to call the day before if possible to allow for corrections. Desert Rock Sports can provide details: http://desertrocksportslv.com/climbinfo.html