The Gypsy Moon (Rocky Jones, Space Ranger II)
'Manhunt in Space' and 'Crash of the Moons' were two of my favorite MST3K episodes, but there are still plenty of Rocky Jones "movies" left to riff, and they're all perfect RiffTrax material. Probably the best one to kick off with would be 'The Gypsy Moon', which occurs before the events of 'Crash of the Moons' and features everybody's favorite gregarious alien... John Banner!
There's also plenty of Winky (some might say far too much Winky), Cleolanta, space friars, and an extremely early version of Google Translate that only works on John Banner.
You can watch a copy of the entire "movie" here: (though the sound isn't great)
Both 'The Gypsy Moon' and 'Menace from Outerspace' have been released on DVD, and as far as I know, are now in the public domain.
You can watch the entire "movie" here.