I've been going the CamelBak route myself. They make a bunch of small packs that pack a couple liters of water and enough room for lunch, an extra layer, spare gloves, etc. without being too bulky. They sell a few that are ski-specific -- you can also get the hose insulation kit separately and add it to any pack that has a hydration bladder. (Although the ski-specific ones have zippered pockets to keep the hose out of the way, which is nice.)
The Platypus bottles are very popular these days, and cheap. I feel like a liter of water in one of my jacket pockets might throw me off, though. With a pack the weight is much more evenly distributed, and on your shoulders.
Wouldn't recommend a Nalgene or other hard water bottle. Those things *will* hurt if you fall on them. A lot.