the keyboard that came with my older mx1000 mouse had a decent range. i was suprised that we got about 40ft out of it through walls. never tried to max out the mouses range though. perhaps look up what type of wireless receiver they used and try to pick something out similar.
a typical wireless mouse has a range of only 4-6 feet or so. keyboards might fare a little better.
as the second poster stated, you could always bring the receiver closer. if you're worried about cable clutter you could always do something like the following:
pc<--->wallplate<--in wall cable-->wallplate<--->receiver
similar to how home theatre systems solve the wire issue.
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searching google for something like i did might help you out also:
http://www.google.com/search?q=long+range+wireless+mouse&hl=en&source=hp&aq=f&aqi=g-c3g-sx1g-msx2g-b4&aql=&oq=
finding a keyboard/mouse meant for media pcs may mean a greater signal reach than normal desktop kb/m combinations.