A wiki website for cataloguing the contents of magazine back-issues.
Information catalogued would include article titles, authors, brief descriptions of contents, advertisements, page numbers... As far as the fan entering the information can handle.
Copyright is obviously the biggest issue. Articles would not be copied word-for-word, but information from articles could be described (eg. "review of CD, review was five starts").
My desire for such a wiki is obviously for the information. Personally I'd love to be able to read every magazine ever searching for the information I want, but an index like this would allow me to focus my efforts.
I'm particularly interested in it's use as a catalog for old gig advertisements. Copyright again gets in the way... it's probably not legal to post direct scans of old gig adverts (as the layout and images would be copyright), however it should be legal to republish the information in those advertisements, as you cannot copyright information.
For example, you could saw a magazine had an advertisement for gigs at the Corner Hotel for bands X on date Y.
Now... go build it, I'm too busy. You make money now OK?
Services like this exist now (RoJaRo is particularly good), but they either hide their information behind a pay-wall (either due to copyright requirements, or to help pay for/justify their cataloguing effort) or have very small amounts of info (eg. page numbers).
Opening it up wiki style might help improve the amount of info available.
Or maybe it would be a complete mess...