Those were both pretty good ones. In the one with Bruce Campbell, he played a demon of some sort who kept killing his newborn children because he wanted a normal human child and his various wives kept bearing demon offispring. He also had a cameo in the Dr. Strange sequel that Marvel did a few years ago, guessing mostly because Sam Raimi ended up directing it.
Alek Trebek and Jesse Ventura played Men in Black in the other episode, which was an alien themed one, and it was almost a fourth wall kind of thing when a characters describes one of the MIB as looking just like Trebek "you mean the Jeopardy show host?", or a line close to that I think. Or he may have been low key playing himself in a goofy role since Chris Carter had an odd sense of humor. And don't forget to include Charles Nelson Reilly to the list of people in that episode. If you don't know who he is, YouTube the old Hollywood Squares show. If you don't remember that, then you have two reasons to YouTube the show.
My two favorites though are a toss up between between one with Peter Boyle and another with Burt Reynolds. Peter Boyle (Young Frankenstein) played a psychic insurance salesman who could sometimes see the future violent, tragic, deaths of some of the people he came in contact with. His visions were very clear, and he saw all of the violence and gore in great detail just like he was watching it play out right in front of him. He could also look at the scene of a violent crime, or touch an associated obect, and describe what had happened down to every gory detail and specific violent act that had occured, again just like he was there and watching it take place right in front of him, to the point that he ended up blowing chunks after 'seeing' the murder take place. He ran into Mulder and Scully at the crime scene of a serial killer who was trying to figure out the reason for his actions while Boyle was also trying to figure out how to deal with all the trauma that came with his "gift".
The Burt Reynolds one was pretty funny, for a while they were doing an episode every so often that was random and wasn't associated with trying to find "the truth", even though it was still the X-Files. This one also involved tracking down a serial killer, numerology, and some kitschiness, but it was fun because Burt's character had that same sort of goofy demeanor that he had back in the Smokey and the Bandit days, and the whole episode was pretty light and fun when the killer wasn't brutalizing his victims. To be honest, I wouldn't have been surprised if Dom DeLouise had randomly showed up at some point since it had that sort of feel, kind of like an old Gumball Rally movie.
Winston