I just found an index of Xena crossover fics. Some of them look like quite a stretch (the movie "Fargo", "Mayberry, RFD), but it looks like a fair amount of entertainment potential.
Stories are grouped by the show/book/movie besides Xena where the story is set, and categorized as gen, het, slash, or alt. In Xena fic, slash refers only to m/m fic (eg, Ares/Joxer), while Xena/Gabrielle and all other f/f couples are referred to as alt. "Uber" refers to stories with characters based on Xena and Gabrielle, with different names, meeting in non-"Xena" times and places.
Xena Crossover Fanfiction Story Index
http://xenawp.org/crossovers.htm