I've thrown these up every once in a while, but for all the new people here are two items you should really look at if you intend of raiding/pvping in MoP.
The first is called the Razer Nostromo (formerly the Belkins N52) that is used for your non-mouse hand. It has 16 hotkeys, a scroll wheel, and a D-Pad. The D-pad allows you to move your character independently of the screen view and strafe much easier. The hotkeys (once you get used to them) become like muscle memory. This is the type of device that lets you stop failing at mechanics that require movement.
The second is a good gaming mouse. I personally use the Razer Naga, but there are plenty of different ones out there. A good gaming mouse will have additional hotkeys in addition to a button for auto-run and vent activation. Again, having all those buttons at your disposal means no more searching or mis-clicks. The more your eyes are on the action on the screen, the more you'll survive.
or the new one with less hotkeys, but a different button pattern
You can find them both discounted at Amazon or Newegg pretty often, and I'll warn you they do take a bit of time to set-up/get used to. But if you intend to keep playing PC games, they are worth the money/time investment.