hpcallipygian has already rec'd this, but I know that there are other Veronica Mars fans on my flist that aren't on his.
booster17 is working on a Buffy/Veronica Mars x-over called
California Screaming and it's pretty rad. I'm not a big VM fan, and already I'm double-checking why, because this is intriguing, intelligent, and hilarious. And you don't even have to be a big VM fan to get into it -
booster17 gives you all the info you really need right up front in a rather charming fashion.
Fair warning, though, it's a WIP, and this is only the first chapter.