The Shatner/Nimoy things are hilarious - I would add Nimoy's If I Had A Hammer to the others mentioned. They were, of course, done tongue-in-cheek. There is an album out there somewhere called Golden Throats, or something like that, that has I think one hundred tracks of stuff like that. A friend of mine has it, if anyone is curious I can ask him about it.
Worst record ever?
I had the misfortune of spotting Sarah Vaughan's "Songs of the Beatles" at my local record store and, intrigued, I bought it since it was only $2. I'm still traumatized a few hours after listening to it; who and why would ever release a record that bad? I love Sarah as a jazz singer but her rendition of the Beatles' songs is absolutely atrocious. I just can't believe someone made a decision to actually release it.