I watched all 11 seasons of Happy Days recently. I'd seen the first 6 seasons before and those are on DVD but I was really surprised that I'd never even seen seasons 7-11, so watching those were like watching a new show!
The show was never the same after Ron Howard left...he was the heart of that show.
There's an episode of Ghost Stories for Christmaswith Christopher Lee — The Ash Tree — which I don't think is available on DVD yet. It'd be nice to see it in good quality. The other three episodes are amongst the extras on the BBC's tie-in box set.