I started off with the Harbor Freight mini air powered belt sander and rarely use it at all after buying the Milwaukee cordless one. That is one tool they got perfect on the first try, it's just incredibly handy and will sand at really low speeds and really high speeds under a heavy load without bogging out like the air one does. It's just so much more controllable.
The 3M Cubitron belts are the shit by the way, don't waste your money on anything else. They keep cutting pretty well until the grit is totally gone and they last forever.