And I found that Mike Nelson, formerly of MST3K, is now making Rifftrax, in much the same style.
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...