1: Astro x Futurama (well that one is obvious)
2: James Bond x Astro ... Q gives 007 a large suitcase with the instructions to only open in case of dire emergency. A new Q has replaced the old one and he looks a bit like

3: Voyage to the Bottom of the sea x Clive Cussler's Numa and Pitt novels
4: Doctor Who x *anything*! (there a a gazillion Dr. Who stories on FF.net)
5: Harry Potter x *anything*! (ditto. But I'm not really into Harry Potter as a fan fiction)
6: Astro x The Jetsons (Now this has some real possibilities! I can see Spacely vs Cogswell in a fight over Astro)
7: Voyage to the bottom of the sea X 20,000 Leagues under the sea (except I think Irwin Allen probably did that already! Also Cussler had Pitt find the Nautilus in one novel)
8: Astro X Forbidden Planet (It would be cool to see Astro interact with Robby. Actually, I have a better idea. Morbius doesn't build Robby, the Krell have left plans for a robot, or Morbius finds a robot built by the Krell in status. That robot IS Astro. )
9: Astro X Lost in Space
10: Astro X Fireball XL5 (or Astro X Supercar) I suspect only AprilSeven, and Jeffbert will remember those two....
Anybody have their own secret crossover story ideas?