Here's a little normal map previewer I wrote a while back for a texture artist. Drag a normal map in png format with power of 2 width and height onto the executable. It should show up lit from the top left, in grey scale. Click to move the light (but don't click outside the black rectangle, I don't remember if I clamped my trig).

If you don't have a normal map to try it out on, grab Monkey Bump. It should work on most graphics cards that support normal mapping at all, and that includes some that don't really support shaders. That is not, however, a guarantee.