This was the best mouse I've used in my computing life.
I miss the symmetrical layout with large forward/back buttons.
Seems like a known defect with this mouse which is a shame, because it was otherwise perfect.
http://www.amazon.com/SteelSeries-Rival-Optical-Gaming-Mouse...
Anker 8200: economical; software-configurable colours (sorry but I cannot stand blue lights, like what some mice are limited to); easily allows switching between 4 levels of precision, which helps when drawing in a graphics editor; forward and backward buttons, which are not only essential in a Web browser, but are also very useful when switching between scroll positions in a long code file; good tracking; and overall a nice feel.
I'm looking to upgrade too. My contenders are the new Logitech MX Master ( http://www.logitech.com/en-us/product/mx-master?crid=7 ) and the Marathon m705.
i prefer smaller, so I'm leaning towards the m705.
The M500 was my favorite mouse for a long time, but due to wrist troubles I'm trying to avoid the mouse altogether an only use the keyboard. I have a Logitech Trackman Marble trackball now. It could be better but there's not a great deal of choice in trackballs.
As for working I couldn't care less what I should use as long as it works fine.
After my G500 broke after a few years of heavy use, I bought a RAT 7, which was terrible. Uncomfortable and a bad sensor. Returned it, got a G500s, couldn't be happier. It's just a good mouse.
Available for ~$20 easily on eBay.
Prior to that, I liked the Microsoft Explorer mice, but they are wired, sadly.
It collects skin, but I find cleaning it grossly enjoyable.