Led Zeppelin's contract prohibited any UK singles, but atlantic US issued some, before Peter Grant intervened. Stairway was never issued as a single, at least not back then.
Pink Floyd just didn't care to promote single songs, since they thought that they were working on concept albums and seperating them spoilt the overall effect. However on albums such as dark side, the wall and final cut the extrordinary success led to many seperate releases on different countries, some of them are quite collectible. Perhaps the only single they released on purpose was another brock 2, due to their being in dire straits. ;-)
Of course Rogerless floyd issued many singles in order to overcome the issue of Roger.