$30 isn't really going to buy you much, to be honest. Koss Portapros are ugly but they're decent for the price range.
If you can stretch the budget, you can get a pair of Grado SR-60s, they're awesome for the money. Alternatively, Sennheisers have some good cans in the sub-$100 range. Other than that though, you're really not spending enough to get into any significantly awesome headphones.