i ride adrenaline 26x2.00's (actual measured size 2.13 inches), but I have the pro dual compound version, and it tips the scales at around 618g. keep in mind advertised numbers can vary by 0.1 to even 2 ounces from the actual tire you're getting. personally i'd love to shave a full pound from my bike just by switching tires... but my tires are pretty light already and I don't want to move away from these adrenalines which have great traction and the middle knobs are great when i'm biking on the road.
i've heard a lot of good things about maxxis crossmarks, seen a bunch of ads in MBA too. i've seen it on pro cross country racing rigs too, although they only might be there because the rider is sponsored by Maxxis.
personally i'd go with the time-proven roll-x pro d2's, which got 4th place in MBA's sept. 2005 trailbike tire comparo.