Originally from http://topgamemouse.com/gaming-mouse-for-fps-and-rts/
MMO’s or another games that have lots and lots of controls is much more enjoyable utilizing a good mouse with plenty of added features, like the Razer Naga, that features a 12-button keypad on the thumb. These games have lots of customizable keys, so putting some on your own mouse-hand will load balance your control scheme.
You should probably get your hand on a few display models, although online shopping will provide you with a larger variety at a potentially cheaper cost. Weight and size play a big role.
I thought I’d envy the Naga for my own playstyle, but it ended up being not big enough and lightweight for my big bear paws. The shape and weight are comfort factors, you will want to pick one that fits your level of comfort.
More at Mouse for MMO