Now available [on Wikipedia](http://en.wikipedia.org/wiki/List_of_fictional_diseases), as pointed to by [kottke](http://kottke.org).
The Motaba virus sounds bad, but the cure — heavy doses of Dustin Hoffman — is arguably worse. Count Choculitis is a recent favorite. See the whole list [here](http://en.wikipedia.org/wiki/List_of_fictional_diseases).