if you play First Person Schooters i recomend a Razer Diamondback or better, you can pick them up for around £30. and then get a standard keyboard from tesco, WH smiths etc...
logitech and other high branded keyboards are over priced and come bundled with lots of software.
Tips:
black keyboards look nicer and stay cleaner
get a keyboard that has a good feel when pressing the buttons
don't get a keyboard with thousands of hot keys, u'll never use
the arm rest is proven to increase risk of wrist strain, try not 2 use one.
if you like the idea of a compact keyboard make sure the function key isn't in the way of normal keys.