I always liked the one that had all the major species running around collecting DNA to discover the "origin species" that seeded all the planets with life, explaining why everyone was bipedal. Can't think of the title.
I concocted my own fan fiction story idea around that. The basis was the alien woman who's hologram appeared explaining what they did, was actually recorded as their homeworld was under a final, devastating attack by a Borg precursor. Seeding the planets was their way of ensuring life would continue after they were wiped out.