the official MS wireless dongle for the Xbox 360 controller is known to overheat and fail over time. some people have claimed the cheap chinese ripoffs of these dongles lasts much longer. take that as you may.
Logitech offers the F710 controller for their wireless solution. however, many a major complaint are forwarded to the dead zones on their analog sticks. it doesn't happen with all the controllers, but you'd be trying your luck.
Razer has the Sabertooth, if i recall. it's a much more expensive x360 controller, with snappier buttons and support for both wired and wireless, from what i read. the cons; expensive.
unfortunately for you, if you want better reliability than the above choices at a reasonable costs, not a lot of choices left for you as wired is still much more reliable than wireless.