I recently moved to Champaign from Chicago, which happens to be a big thrifting town; as an expensive place to live, it is thankfully and inexpensive place to get dressed. While Central Illinois has not revealed all of its thrifting potentials to me yet, my first (and usually last) stop for a wardrobe update is Plato's Closet.
As a resale shop, Plato's goes through a lot of volume and there is always something new. All of their stuff is clean, high-quality and youthful. They are particularly geared to the 25-34 age bracket with good everyday, occasion and professional wear. This location really benefits from the college-town setting with people at all levels of professionalism, and I happen to have particularly good luck finding dresses, blazers and cardigans.
They have a wide variety of dress pants, dresses, jeans, bags, shoes, basics and coats depending on the season. They have descent trade-in options: they pay in cash but usually the in-store credit is a better deal. The frequent buyer/seller card doesn't hurt either. For example, tops and blouses usually cost $6 and dresses typically run $8-15.
Things are tightly packed in the store, but well organized which helps to keep you on the hunt. If don't find what you want, in helps that TJ Maxx is right next door. I highly recommend this place for the graduate student on the budget as a good way to look up-to-date and professional without having to cave to mall retail prices.