A couple that spring to mind are Marvyn Cox at the first bend at Oxford, his forks or frame collapsed I think, and he went straight into the fence, got up with the bike in a few pieces around him. The commentator Peter York went up to him to get his reaction in went something like "****ing hell, my bike!!!".
I also remember Jens Rasmussen having some big crashes one in particular at Oxford was a day meeting (Possibly pairs or 4TT). Looked pretty bad, carried off I think, then the bike a revvin emerges from the pits to a huge roar. He was one tough rider!