Like they said, its probably about time for a new one. Although, to get anything other than a Thompson don't you have to have a mod chip installed, or load drivers for it onto your hard drive, which requires unlocking it? If you don't want to mess with anything like that, you could just order a new Thompson for about 50 bucks. That should last you at least another couple years. Maybe i'm wrong about the drivers or what not, though.
http://www.llamma.com/xbox/parts.htm sells every Xbox part out there. They also sell some new Phillips and Samsung dvd drives.