Here's the problem posed by John Holbo: If I link to a web URL today, and it dies tomorrow, is there any way by which I (and my readers) can still get the contents of that URL? In other words, are there sites which archive web pages with their date stamps?
Crooked Timber readers have provided several pointers (there is a side discussion about tiny-url which can be skipped). WebCite seems to be particularly interesting. Wayback machine is another. On the other hand, Google cache is totally useless for this purpose. One of the perceptive commenters even offers a free business idea for a web service called Content Cryogenics!