I agree with AMKR, more Joe Don Baker material please! He and Adam West have done numerous low budget films which have enough expired rights and limited distribution to make it into the VOD section on the site here.
Overall, there are too many movies on here that I personally think stink even with the commentary. For now, we just need more SciFi-Action blockbusters riffed as well as any turkey or passable gem starring Nicolas Cage, John Travolta or Tom Cruise that hasn't been done yet.
Barbarella would be an interesting one as would be Ghosts of Mars, the Teenage Mutant Ninja Turtles trilogy, Barb Wire, Prometheus and anything Chuck Norris has done.
How about more Ator movies?
NOTE: A riff for Starship Troopers would be pathetic since the film itself is a satire not a mindless alien invasion type movie.