Still using the MX510, have been for years - when it goes, there's a 518 waiting to take its place.
Logitech have got the market cornered for gaming mice, there's very few other mice that seriously rival their range.
One thing that's worth doing is getting a chance to actually feel one - That big PC store will sometimes have a few on display, otherwise asking a friend to use theirs can avoid an expensive mistake. It happened to me once, I bought a G15 to replace my broken Zboard - used it for 10 mins, couldn't get on with it at all, so it had to go back.