Wahl makes the best hair clippers. I've used a sturdy little Wahl Peanut as a beard trimmer for a couple of years. I even cut my hair with it when I'm drunk, which conveniently happens at least once every six weeks.
But Wahl also sells a cordless version that seems to get high marks. The Wahl Rechargeable Hair Clipper even has a rotating head on a ninety-degree handle so it's easier to trim both sides of your hair evenly. Or you could just do what I do: embrace having a horrible haircut.
The Wahl Rechargeable is available in lots of places for a wide range of prices, but it looks like $30 at Amazon is a pretty decent deal.