Logitech USB Optical mouse mate, mine (as I just observed) has molten chocolate and solidified dust on it, no bother at all, from memory about 20 squid. Depends a bit on your PC I think - it seems to me your CPU speed matters with optical mice... low speed CPUs seem to have cursors that go all over the place - my old AMD 475 laptop is useless with an optical mouse, as was an AMD 1200, but AMD 1800 and 2400 based machines were no trouble.
Optical mouse, cheap as you like, 10 quid, never have to clean your balls again. For that added luxury , get a radio one, another tenner, but get one that has rechargeable batteries and a charger base...
I actually have a radio mouse an' all. Not bad actually, I tend to stick to Logitech and Microsoft stuff myself, I find these two brands pretty reliable - I hate to say it, but you seem to get good stuff for your squids whilst supporting Mr Gates in the style he has become accustomed to. Logitech also, from experience, is usually pretty trouble free. On slower PCs I found optical mice would sometimes produce cursor movement opposite to the mouse movement, random jumps onscreen, and so on.... rollerball versions worked fine.
Throw it in the bin or out the window. Then spend a tenner and get an optical one. You'll neve have to clean your balls again IF you fancy a wireless optical, get one that is fitted with rechargable batteries....