pretty much any keyboard and mouse can be used for gaming. you absolutely do not need to spend a great deal of money on a keyboard or mouse if you dont want to.
some things to look for:
-keyboards and mice with a matte finish and not a glossy finish. or else when you sweat your fingers will slip around which isnt good.
-optical mice are preferred for most users. i would say at least 800dpi but you really dont need any more than 1200dpi.
-standard sized or large sized mouse with standard 2 button, scroll wheel configuration.
-both keyboard and mouse i would suggest to be ps/2 or at least usb with a ps/2 adapter.
-full sized keyboard. personally i prefer full depth keys on mine.
-use a standard rubber/foam mousepad not some gaming pad...