Justin asked what settings I used for the pic below.
Camera: Canon Digital Rebel, XTI @ 100 ISO in Manual mode. "Bulb" exposure. Manual shutter release, five second exposure.
Lens: 24-70mm 2.8L at 67mm focal length, stopped down to f10.
Tripod: Hakuba HG-503MX with factory head.
I chose f10 and ISO 100 because fireworks are actually quite bright, and I wanted exposures several seconds long to get enough "action" in the shot.
More of the (as always, full resolution!) pics are at this 4th of July Flickr set