all of the Money in the Bank title changes that did not occur on PPV have been pretty surprising. i'm thinking like Edge beating the Undertaker on Smackdown, CM Punk beating Edge on Raw and the latest with Jack Swagger beating Chris Jericho on Smackdown. they've all been pretty crazy, though obviously no build up or history, and so have not been as "big" as some of the others.
previous posters have given some good ones: Santino winning the IC title in his first match with the WWE and over Umaga no less in the "Milan Miracle", Kurt Angle winning the vacant world title in a Smackdown Battle Royal, Goldberg and Luger over Hogan on Nitro and my personal favorite of Mankind over Rock on Raw in December of 1998.
of the ones not previously listed, i'd have to say that another great one was Marty Janetty vs. Shawn Michaels for the IC title on Raw. that was a great match and i believe Shawn's first in a long line of "Match of the Year" winners.
i also think that Flair's 16th recognized world title reign was on a Monday Nitro, and if that is the case, that'd be considered if only because since then he has gone around as the "16 time world champion" which is a significant accomplishment.
there were also some great title matches with RVD on Raw, against Tommy Dreamer to unify the Hardcore and IC titles and against Christian in a ladder match for the IC title.
two fun ones were when Kane made a return to action and won the Tag Team titles with Hurricane on one Raw and the next week on Raw won the IC title from Chris Jericho. two titles in two Raw appearances and on a clear path to domination. it was so awesome. the match with Hurricane was great when it ended with both giving a chokeslam to the other team, but that match with Chris Jericho was actually very good. great story told and a very exciting match thru and thru.