SkyBus is famous for its $10 fares, but seats are limited and sell out quickly. So to launch 2008 they've opened up a batch of new $20.08 fares for many travel dates. These, too, will go fast, so act now. Columbus to Oakland, for example, is now $40 round-trip, but only for travel in Jan and Feb. After that, some seats are as much as $300-$370 RT. Search flights.
By the way, SkyBus has first come first seated seating, but for an additional $10 you get the board the plane first and get first dibs at prime seats.