Check out the Marmot Hydrogen, also on sale at REI. It's also a great bag, and, like Phat, I'd recommend a down bag without question. It doesn't take that much care or thought to keep a bag - synthetic or down - dry.

The 30-degree rating will still keep you warm down to freezing - if it gets colder, wear your fleece and/or long underwear inside. (If you're a beginner, don't go out below freezing for a while - get some experience. Winter is fun, but it is an acquired taste.)