In my opinion one of the best aspects of Princes music is his use of vocals and background vocals, and the effects he uses on them. Especially in the eighties that was part of his 'trademark' i think. He did create some splendid music with combining distorded background vocals with a more 'natural' clean sounding lead vocals, and vice versa. The use of multitracked vocals (often in a different key, atmosphere) obviously has had much influence on his copy-cats, and the way music 'sounds' today.

Right now this are some favorite examples:

Positivity: 'Don't kiss the beast, be superior at least', Prince is singing this in a very low range, he seems to use some distortion effect on this, that makes my speakers 'bounce', it sounds great. He uses an effect like this on Style (from Emancipation) also.

If i was your girlfriend - Those distored background vocals, in various keys, adding up to the intimate, obsessed atmosphere of the lyrics and music

When doves cry - the cold, detached sounding background vocals adding up to the atmosphere of desperation.

Animal Kingdom - Prince uses some kind of 'echo' that reminds me a lot of John Lennons material in an 'over the top' way. I know, many can stand this song because of the lyrics, but i love the way these vocals sound. He did use this Lennon-like effect on earlier songs like DMSR and Pop Life also.

Lovesexy - Those weird sounding vocals near the end of the song, pitching down and up in tone, adding up to the manic, obsessed sounding music and message. Some of Princes best material in my opinion has the 'quality' that he seens totally obsessed, absorbed, manic almost about what he is trying to say, his use of (background) vocals putting emphasis on, strengthen that feeling or message.

Bob George - The deep, distorded voice, combined with the 'black humor' of the lyrics, leads to something both humorous and grim.

Adore - mixing 'cute, beautifull' background vocals with distored, colder sounding background vocals.

Camille - The introduction of Camille is a masterstroke in my opinion. It brought a depth to Princes music that i have never heart before or after in his music. Not only does this 'voice' sounds great: original, creepy and alienating. Prince uses it to sing more complicated, thoughtfull lyrics
about 'relationships' (with women, friends, drugs and the world around him) and alltough the Camille-voice sounds strange, i always thought the songs sung by Camille are telling me more about the person 'Prince', then most of his other music does. Maybe thats why 'Sign of the Times' is my (and many others: fans, music critic) favorite Prince record: he seems to sing about 'himselve', letting you take a look inside his mind and thoughts, adding a touch of depth and intimacy to the music. Something that makes the different between good music and art.

you're right

also give "Automatic" a listen with headphones on
he's got voices all over each other, in, out, and around the ear

Don't forget Erotic City! The layers of high and low voice effects in that song give me goose bumps. Especially the bootleg version on The Work where he sings in very high falsetto at 3:05 into the song, "erotic city can't you see..." (Sigh)...that part gets me every time!

Not keen on the voice effects that run through TRC. The speeded up background vocals of 1+1+1=3 are cool.