Megabus currently serves select midwest cities such as Minneapolis/St.Paul, Milwaukee, Chicago, Indianapolis, Detroit, Cleveland and Cincinnati. If you purchase in advance, you can get fares for $1 plus a 50 cent booking fee. The prices are relatively cheap even on short-notice trips. Don't live in the Midwest? Megabus will soon be expanding on a national scale.

Site is usually down in the evenings I've noticed.