More info on what you want/expect out of a pack would help those giving advice. If you are currently using a jansport model, you might want to be carefull about jumping to a full-on ultralight pack - even the ones with frames are going to be different than a full-suspension non-UL pack. There's nothing wrong with UL packs, they're just going to be different than what you are used to.
I have a North Face Skareb 55 that weigh 3.5 lbs, and has between 3000-3600ci dependin on size. My large 3650ci has plenty of room for snow camping gear. For the weight with a full suspension, its a pretty good pack, and being North Face, often on sale. Otherwise, a ULA Catalyst might fit the bill. It's lighter than my Skareb and has more volume. You'd also be buying American-made if that makes a difference. One of the new REI UL packs or one of the various Osprey lines are nice too. Anything you can buy at REI or Backcountry.com has the advantage of a 100% return guarantee, even after use. That's a handy piece of mind if you're new to backpacking and not sure what you're looking for.
As pointed out, it comes down to features. Do you want lots of pockets, bulletproof durability; are you willing to sacrifice a tiny bit of carry comfort (and I mean just a tiny little bit) for significantly lighter weight? What do you want?