As for DVD, I have old editions of some Charlie Chaplin films released in 2000 on DVD (based on the terrific 1992-1993 laserdiscs). They were taken out of print in favor of "special editions" which used poor quality PAL-to-NTSC conversions. I also had a rare 4-disc Beatles set (including Help! and Magical Mystery Tour), but I opted to sell it for $150 and burn myself some copies. There's also the matter of a lot of Disney stuff that they took out of print.

On VHS, my prize for a while was the original SP tape for UHF. Now the DVD is out, it's worthless. For a while, I had an SP tape of the MST3K episode Gorgo (which aired only once), but it was stolen from my collection.