I love my
Spudz 18% gray microfiber cloth - I have it hooked to my camera strap on the left side of the camera, where it is not in the way. It weighs virtually nothing and it's a perfect location to just pull the cloth out of the bottom and wipe off the lens, LCD, whatever. Plus if you're in a situation where it's going to be difficult to get the white balance correct, it doubles at an 18% gray card.
GameStop sells a
smaller version for about $2 that's marketed for Sony PSP cleaning - I almost got one but I think it's probably a little too small for my tastes, but others might like it even better. It is certainly plenty cheap.
Another terrific product that's not too expensive is the
Op/Tech Pro Strap, it makes your camera feel significantly lighter. This is a great size for DSLRs; for a smaller PnS, they make smaller versions.
Then there's camera bags... tripod bags and/or straps... a new ball head or pan head for your tripod... a Clamperpod or Gorillapod... an instructional book (specific for your camera if one exists)... etc, etc.