Thrift stores! I can't say enough about how awesome thrift stores are. Name brands, great prices, and tons of different cuts so you're almost guaranteed to find something that's right for your body.
I recently bagged up all my too-big summer clothes, and when I went to try on my autumn/winter clothes, I discovered none of those fit either. It was time to go shopping or go naked.
Two thrift stores and about $50 and I have a whole new wardrobe that will hopefully last me through most of the winter. (My major score was four pairs of corduroys that are like new, fit me like a dream (low rise, boot cut), and are name brands - for $3 each! And cords are versatile enough for office wear or casual wear.)
ETA: Like caryesings, I don't belong in the 20-somethings. But it's a universal issue!