Those of you more connected to MST3K than I am will deride me for being so out of touch, of course, but better late than never.
Since the MST3K crew reunited as The Film Crew, I've come to realize how much I missed MST3K. I also managed to connect to a bit of my own personal history having found some clips of Disasterpiece Theatre, which was an MST3K like show that aired on XETV in San Diego when I was 12. I used to stay up way late to watch Sal U. Lloyd and The Other Guy skewer bad 50s B movies. They mostly used chroma keying and Chyron rather than voiceovers, but it was still funny stuff.
Anyway, by chance I managed to learn that Mike Nelson came up with a compromise allowing him and his co-riffers to skewer movies without having to actually obtain rights to them. How? By writing and performing commentary tracks that you play along with the movie. Of course, you need to synchronize the two streams, but they have a pretty ingenious method for doing so - a disembodied computer-like voice periodically chimes in during the commentary with lines from the movie that should synchronize precisely with an actor in the movie delivering the same line. If the movie line is late, you pause the commentary for a little bit. If the movie is early, pause the movie. It even works with Netflix's instant watching feature (I tried The Matrix).
Keeping them in sync isn't as hard (or as critical) as it sounds, and the riffing is just as good as it ever was on MST3K or The Film Crew. And to top it all off, the RiffTrax are for movies you've actually heard of!
Go check it out. Most of them are either $2.99 or $3.99 and they're DRM-free MP3 files.