Here's a Voyager/multiple fic-verse Crossover Fic I'm working on:
Star Trek: Voyager - Dark Realm
(Shameless self promotion, I know).
Here are some good ones from Fanfiction.net. The first is a multi-chapter fic. The second is a nice little one-shot for those of us on the go.
Back and Forth - A Bajoran's Tale
(A Celes Tal and Seven of Nine femslash fic)
[The next one is over PG13 - Warning]
My Sweet Screwup
(A Celes Tal and Janeway femslash fic)