Well, some cheap keyboards suck. Some are really springy and hard to type on, and some have poor feel so you don't always know if your keypress has been registered. The thing is, it's all a matter of personal feel and preference. Some people like really flat keybaords, some like ergonimically shaped ones, some like stiff keys with a positive click, some like a light touch. Some keyboards have multimedia keys, which can be great if you use that sort of thing. If you type fast and type a lot, a good keyboard can make a big difference; if you hunt and peck, then it probably won't matter much. I think the best way is to run over to Best Buy or Circuit City or something and try them out; then order online.
Mouse feel can be the same. Some are really precise, while others less so. Some are specially shaped, which is great if it fits your hand but could give you cramps if it doesn't. Again, it's really a matter of personal feel.