I second Champion, I like their stuff, not sure the size range available though. If you have a bit of money to spend, look at Junonia.com. If not, check out Lane Bryant Catalog (separate from the store) and Roaman's catalog. Both are online as well. The clothes are cheap -- and cheap -- but you're not going to be in that size for long, eh?
Also, Catherines and Avenue might be worth investigating; if there are no stores in your area, I believe they also do some online sales.