A Panther XL works great in UT, and HL,Q2,Q3 for that matter. It'a a joystick trackball combo. Stick in the right hand for movement and weapons etc , trackball in left used to "look" and a few more buttons to play with. Sadly out of production
but the PXL Pro is eagerly awaited.
Other than that alot of people use a joystick/trackball combo (separate pieces) a Saitek or CH F16 stick with a Kensington Expert Mouse Pro or cheapie Crystal Trackball seems to work well.
But to be honest it all comes down to what you find most comfortable.