You mentioned Queen earlier. A favourite B-side of mine is their See What A Fool I've Been (b-side to Seven Seas of Rhye), for my money one of their best ever songs.
Submarine by Genesis is an unusual and atmospheric instrumental that was b-side to Man On The Corner.
XTC and Radiohead are two favourite bands of mine that have an abundance of superb quality b-sides, so much so I'm not sure which ones I'd pick out.
Thanks. I had most Queen albums and a few singles but I'll need to look up See What A Fool I've Been on youtube as I can't immediately remember it. Was it taken from one of the first two Queen albums