I couldn't agree more with Clive about the Goldberg Variations. If I was only allowed one piece on that desert island, I think it would have to be the Goldberg (although possibly the B minor Mass or Mozart's C minor Mass).
I also agree with him about Dimitry Sitkovetsky's string trio arrangement, which grew on me, too.
(This is the perfect cue for me to reveal one of the greatest pieces of trivia I know. Stand by to be amazed. Astonished, even. Flabbergasted.
Dimitry Sitkovetsky has been to watch Chelsea play with this man.
Told you it was good.)
But if we're talking about adaptations, nothing comes close in my mind to Uri Caine's. I can't recommend it too highly - it's on Amazon here.
As for piano recorings: this Glenn Gould CD, which contains both his 1955 and 1981 recordings, is the steal of the century at £9.99, since either recording on their own would be worth ten times that. No music collection is acceptable without Gould's Goldberg!
There any other number of fine recordings - Andras Schiff, Murray Perahia et al. But the one I find myself listening to repeatedly is Angela Hewitt. In the days when I reviewed CDs, I came home with a batch of new CDs after a long evening out and put on Hewitt's recording to hear the first few variations. Eighty minutes later I took the CD out, having been held in total wonderment at her recording. It really is as fine as any recording of anything I've ever heard.