I've had an Osprey Ceres 50 for about a month now, and it is everything I've wanted in a pack. It's really comfortable, 3000 in3, under 4 lbs, well built, and has lots of space for two tools, a shovel, pad, skis, snowshoes, etc. (you could take all at the same time if you really wanted to.) Check it out at:
http://www.ospreypacks.com/ceres50.html