1. For You (1978)Prince's debut album, the one that gave us "Soft and Wet," has been left high and dry out of the iTunes catalog. Maybe Prince doesn't like his puffed-out fro on the cover; maybe this second-rate Sylvester impersonation played better when everyone thought he was a 19-year-old wunderkind instead of a 21-year-old shaving years off his official bio.
Whatever the reason, the only Prince album worth owning for purely historical reasons isn't worth owning — or possible to own — digitally.
2. Love Symbol Album (1994)The album where he changed his name to an unpronounceable symbol. If you buy just one Prince album in which he converses with Kirstie Alley between songs, make it this one.
3. The Black Album (1994)Withdrawn from release in 1988 and replaced with Lovesexy only to become one of the most bootlegged albums of all time, Prince's Black Album saw a quiet official release in 1994 but remains unavailable digitally.
Maybe Spinal Tap saw the all-black cover and issued a cease-and-desist.
4. The Gold Experience (1995)A concept album and cut-for-cut probably Prince's strongest since Sign "O" the Times. Here's where his relationship with Warner Brothers went south, as evidenced by tracks like "Eye Hate U."
Curiously, Come, a 1994 collection of tracks recorded at the same time as The Gold Experience that Prince himself disowned at release, is available on iTunes.