Your favorite one-man band!

stevie wonder plays everything except guitar on his best records...
skip spence played all the instruments on the outside classic "oar"

Maxnewid,

Funny you should mention Todd Rundgren.  On his record A Capella, every sound is Todd's voice (often electrically manipulated).  It's kind of an ultimate "one man band" in that he needs zero strings (or keys, or anything else).

That album also contains one of IMO the most beatiful ballads of the pop/rock era - "Pretending to Care".  Ironically, the version on A Capella isn't my favorite, but it's certainly an ambitious take on the song.

Jackson Browne. I know he usually has a band, but he did a series of "Solo Acoustic" albums and shows. I saw him, in concert,  twice during this time.

FANTASTIC shows and music!

I back HAROLD-NOT-THE-BARREL: Tubular Bells by Mike Oldfield!!!
Jean-Michel Jarre also but it is not quite the same, practically all Electronic Music is a "one man band", I have so many favorites here that dont know where to start: Jarre or Klaus Schulze, or Pyramid Peak, or Der Spyra, dunno

Jon Brion.