I am looking for a good, light tire for my mountain bike with 26 inch wheels. Intended usage will be for occasional cyclocross races and long XC rides. Something under 2" is what I want since I already have a tire that I like in 2".
Depends on what terrain you ride. The big S has a good tire in the Purgatory in a 1.9 flavor. I run one out back on my Epic and it hooks up great in all conditions. Maxxis also makes some decent stuff too. The Ignitor comes in a 1.95 flavor.
For the front, I am a big front WIDE tire guy. Like pushing the front end into corners too much and want as much MEAT up front as I can get. As close to 2.4s as I can get generally...
If low weight is a priority, you could also check out the various Supersonic models from Continental. In a 1.9", there's the Twister at about 370 grams: http://www.conti-online.com/generato...wister_en.html If you wanted a bit more tread, the Speed King Supersonic is their next-treadier one. If you're going this route, make sure to pick the Supersonic and not one of the other variants.
Scwalbe's Furious Fred 2.0 (about a 1.8 in reality) is even lighter, around 330 grams, and tubeless-ready. Not much tread, though... best for frozen or tacky-to-almost-dry conditions. I have a set of those and they get saved for when the time is right. A CX race would fit the bill, but not a pedal-to-the-metal XC race... just not enough volume to protect the rims, I need something like an honest 2.2-2.3 for that.
the old Maxis Minitaur 380 was a tire that garnered as many bad reviews as good. I recently tried a pair that i have had new in the box since 2005. I actually had great success at XC riding with it. Don't know how easy it is to find them but if you can they are probably cheap
1984 Bianchi San Remo, On-One Inbred 456 Summer Season
I haven't tried any of the tires that these other guys have suggested, so I can't really compare, but one that I have tried is the WTB Wolverine. I have the 26x2.2 Race version as a rear tire and its been great. I love the lack of rolling resistance on this tire, and it's pretty big for a 2.2. They do make a smaller version, although I'm not exactly sure what size it is at the moment, either a 2.0 or 1.95 I think.