Geri "Ginger Spice" Halliwell plays Chev's mother in the second movie.
Also in the second movie, Q is the news reporter. John de Lancie even uses his Q method of delivery for the bits, so it's almost impossible not to think of it as Q futzing around with history to amuse himself. (It would be one of the least nonsensical things in the sequel.)
Several porn stars, including Ron Jeremy, have cameos in the second movie.
Sam Witwer has a cameo as a thug in the first movie.
Maynard James Keenan (of Tool and A Perfect Circle) and Danny Lohner (also from APC) cameo in the second film as two guys who use a shock collar on their dog. Chelios gets them to use the shock collar on him.