The last crossover fic I ever read (and truly liked as well) was Mass Effect: Renegade. The writer crossed the Mass Effect universe over with the Command & Conquer universe's Tiberium timeline. The result? The Systems Alliance being replaced by GDI, The Reapers taking place of the Scrin, Nod spreading their organization throughout the stars, and the Citadel species drastically changing their approach towards humans and military viewpoints as well.
And the crazy thing? A part of me wants to see this crossover happen because both universes could fit each other quite well, and to top it off EA AND Bioware now owns the rights for both, meaning that it could totally happen!
edited 11th Jul '12 3:02:07 AM by SgtRicko
Would you believe I never fully watched the original Indiana Jones trilogy? I gotta correct that someday.