I recently came across a new webcomic, Faraday the Blob (new to me, that is). One of the weirder things, when reading the archives, is that the author has independently come up with a joke I came up with, the HP Lovecraft printer. Maybe it's not that creative a pun (and his illustrated box cover for it has some great cleverness, like the colour stats on the printer are "Colours out of Space"). Seeing this kind of independent recreation of humour makes me want to see (or at least imagine/design) some kind of a site that finds independent convergent creations of quips and ideas and puts them side-by-side. Maybe that's what TVTropes is about, for stories.
I suppose it'd be hard to verify what's really uninspired by other things; people either might not be entirely honest, or they might forget their inspirations. I remember being terribly embarassed that one of my prior named sketch ideas ended up with a similar name to another webcomic I used to read. I only realised it a few months after I put the sketch online.