The giant table of road signs is a pictorial index to all the signs I have. The page contains about 1MB of images; so for representative samples check out:
You can download all 300+ road signs, in EPS and PNG format, as either one 9MB .zip file or one 8MB .tgz file.
You can read a bit more about road signs and this project at my about road signs page.
The original EPS files of these road signs were extracted from the US Department of Transportation MUTCD. According to the MUTCD FAQ, "All devices included in the MUTCD...are in the public domain. They are available for reproduction without prior approval, except for the Interstate route signs, which must be approved by AASHTO." Because of this, I can offer all these signs under my Free License.