More Issues and Attributes
Thresh's comments in BLACK
Kenn's comments in BLUE
When purchasing a keyboard, make sure the keyboard connector is of the same type your computer uses. In other words, if you have an AT-style case, get a keyboard with an AT style connector. Likewise, if you have an ATX or PS/2 style case, get a keyboard with a PS/2 style connector. Most new keyboards come with a PS/2 connector as default, and some like the Microsoft Natural Keyboard Elite also come with a USB connector. You might want to avoid using converters to switch between connector types, as they are more likely to come loose or get unplugged or lost in various situations.
Other nuances I pay attention to are the size and shape of the Enter key (oversized Enter keys and L-shape Enter keys are easier to press), the size of the Backspace key (some keyboards have tiny Backspace keys), and the Cursor keys layout. Most keyboards have the cursor keys arranged in an Inverted-T, while others have cursor keys laid out like a cross (like the numeric keyboard cursor keys).
I personally like the "inverted T" the most. Though not used much in FPS games, the standard "WASD" configuration is essentially the same thing. In general, standard is good.
For gaming, try to stay away from keyboards such as the Microsoft Natural Elite; not only are the cursor and F-keys notebook-small, they're also placed in a non-standard "cross" formation. Weird.
I've noticed quite a few "ergonomic" keyboards out there, designed to reduce Carpal Tunnel Syndrome (CTS). CTS is an injury which results from typing or moving the mouse too much. While ergonomic keyboards are easier on the wrists, they tend to suck for games. This is because they're usually split vertically in the middle for better hand positioning. With one hand on the mouse, it is damn near impossible to reach some keys on the right side, such as the railgun for Quake 2 (or the various teamplay binds scattered along the F-keys and right side).