I'd recommend a Logitech MX300 mouse.
It's a basic two-button plus scroll mouse, fits in either hand, but uses the fantastic Logitech MX sensor circuitry. Very responsive even at high mouse speeds (better than most other mice) and no lag.
I have one at work and love it.
Plus, it has a little button just behind the left/right which can be programmed to activate Exposé. No driver required.