At 4+ you can do the full WPPSI-IV test (we did the under 4 edition which is a bit more limited). Even so we found the results helpful. You can't take the WISC till 6+ I think.

Hoagies has a state by state list of testers here:
http://www.hoagiesgifted.org/psychologists.htm

We are going the Gifted Private school route (and I agree that spending a few hundred on testing can be money very well spent if it helps avoid a lost year(s) for a child).