I agree with mojokey. Or you could recreate it with a torus primitive and delete the unwanted geo. Make sure "generate Mapping Coords." is checked on before converting it from a primitive to edit poly. Or if you're really bent on unwrapping it as is you can straighten it out pretty quickly by: Click a vertical edge, click…
If you didn't unwrap it prior to the bend, you can get pretty good results by using the pelt tool followed by relax. Just put a seam down the side and around the caps, use pelt to pull it out, then relax to revert it to a squarish shape. then you can use the align-vertical/align-horizontal tools to straighten out the outer…