Seasons 2 and 3 of GG in particular are awesome, and Jess/Rory is my favourite tv ship ever! I'm up to S6 at the moment, and as soon as I've finished, I'm going back to S2 and watching from Jess' arrival again.

Nathan/Lorelai would be really interesting - I think he likes women he can shut up a bit more easily though. I've always liked the idea of Jess/Claire and Rory/Peter crossover fics, but I think that's because they still get Milo - just with a different name...