Not sure if this entirely fits this category, but it's at least related. I have a vinyl copy of Joe Jackson's "Big World," which is a 3-sided album. What, you say? Indeed. The album is actually a double album. Album 1 has tracks on both sides. Album 2, however, has tracks on only one side; the other side simply contains a groove with no recorded sound. Thus, the record "plays" like any other record, though there's nothing to be heard. (By the way, all of you dB's fans who are frustrated at not being able to find "Like This" or "The Sound of Music" or who have paid exorbitant prices for such on eBay, I recently purchased this Joe Jackson recording on CD for upwards of $100 from a seller in Japan.)

I had a similar three sided album by Keith Jarrett. Unfortunately it was lost subsequent to a break up with an old girlfriend. Also lost was my original copy of The Beatles with Tony Sheridan on Savage Records AND my Paul McCartney Intervew Album. A painful memory....

Lest we forget "Second Winter" by Johnny Winter with the blank 4th side. Remember Columbia's ill-fated $.99 one sided singles?

"It's a Gas", a cardboard-pressed record that came free in copies of Mad Magazine (1965?), had double grooves, although I think it was only at the end of the "song" (a stock sixties instrumental with belches every once in a while) and didn't really work, if I recall correctly -- once the needle had gotten used to going with one of the two grooves, it wanted to go to it every time.