Frank Zappa

[progdirjim(Admin)]

"Hot Rats" is almost entirely instrumental, except for some vox on "Willie the Pimp". which also includes some great jamming. It's a solid first choice for prog fans.
"Jazz From Hell" has a much more modern sound - Frank plays synclavier and no guitar - fairly complex, another good chice.
"Waka Jawaka" is another solid prog choice, from the same period as "Hot Rats". Few vocals, and not the most controversial ones.
"The Grand Wazoo" has vocals only on "Calvin and his next 2 hitchhickers", and they only last a minute or two into an eccentric jazzy piece. Another good choice as long as you don't mind some serious jazz leanings.

Try those and if you want more suggestions after that, post again and we'll work you into the vocals...