I will have to second the Microsoft mouse choice...sad I know. I had to get a new mouse for 3D work recently, and the MS one just 'felt' best to me, but I guess that depends on the shape/size of your hands and what you are used to.
Also, the middle button was really important to me (again, for the type of work I do), so I was looking for a mouse with a 'smooth' middle button/scroll wheel.
Best thing to do is to go to a store with a good selection of mice and check them out for yourself...try before you buy