I got the cheapest mouse at Office Depot. $15 for an optical USB wheel mouse with vertical sides. That's all I wanted. Nothing fancy, not wireless, not sloped sides. My current mouse at work has sloped sides, and when I have to pick it up, it's a pain. The big problem with this MS mouse is the wheel. I use the button under the wheel as a middle-click. In Firefox, I have it set to open a web page in a new browser tab. In Linux terminal windows, it does a Paste. Needless to say, I hit that button a lot.
The problem is that with the MS Basic Optical Mouse, a middle click often results in some unintended rotation of the wheel. This means that I miss the link I want to click on and instead paste into my browser window, which tells it to load a new web page. If they cannot make a depressable wheel, they shouldn't be in the mouse business.