The keyboard and mouse you use are important choices when designing a computer, as they are the only parts of a system you touch on a regular basis (and almost constantly while using the computer). Having a keyboard that is comfortable and responsive makes for a pleasant experience. Wireless models are often more convenient than wired, since you don't have as many cables cluttering your work area - but some people claim to notice a small lag between typing and having the computer register keystrokes, so it isn't for everyone.
The options we provide at Puget are either stand-alone keyboards or kits with both a keyboard and a mouse (look for the terms 'pack' or 'combo'). If you pick a keyboard by itself then you may also want to select a mouse in the next category down.