And I found that Mike Nelson, formerly of MST3K, is now making Rifftrax, in much the same style.
http://www.rifftrax.com/
For popular movies, you can download the mp3 file and play it synced with your DVD (manually or using the Windows-only Rifftrax Player). For public domain movies, you can download or stream them pre-synced. You can even upload your own tracks to sell.
I'm looking forward to watching new-and-improved Twilight. I thought it was funny the first time I watched it...