Well, not having ever watched Eureka, I can't say whether they meet your criteria (especially length), but I have come accross a few fics that I've
found enjoyable. Only one isn't a crossover, and it's a series of connected drabbles, I'm afraid.
Willow Rosenberg: the Typical, Normal Teenager
by dulcinea
Following the "Gingerbread" episode, Willow and her parents realize they don't know each other as well as they had thought... starting with
their real names.
No Place Like Eureka by jedibuttercup
She seemed familiar to Nathan somehow, but not enough to account for the expression of disbelieving hope on her face.
Eureka Moments by jedibuttercup
Tag scenes for EUReKA SEASON 3
found enjoyable. Only one isn't a crossover, and it's a series of connected drabbles, I'm afraid.
Willow Rosenberg: the Typical, Normal Teenager
by dulcinea
Following the "Gingerbread" episode, Willow and her parents realize they don't know each other as well as they had thought... starting with
their real names.
No Place Like Eureka by jedibuttercup
She seemed familiar to Nathan somehow, but not enough to account for the expression of disbelieving hope on her face.
Eureka Moments by jedibuttercup
Tag scenes for EUReKA SEASON 3