I was surprised to learn that members of TOTO (they were highly sought after session musicians before and after forming TOTO) played extensively on The Wall. Apparently, the story goes that Roger Waters was annoyed with Gilmour and company's inability to get "the mood" of Water's masterpieces, so he brings in Jeff Pecaro and Steve Luthaka (Pecaro is credited while Luthaka is uncredited). If you play early TOTO (circa 1979 Hold The Line and I'll Suplly The Love) you'll hear elements of Another Brick In The Wall and Run Like Hell. Pecaro's contribution to precise synchopated drumming is loud and clear on the Wall.
Toni Tennille and Bruce Johnston of the Beach Boys also did backing vocals on The Well.