Most of these were just for my own self amusement, but I think I ended up with;
Mass effect/Thunderbirds
Primeval/NCIS
Primeval/Law & Order SVU
Harry Potter/Thunderbirds
Bull/Law & Order SVU
And a long time ago there was a Matrix does HIGNFY and Matrix does Scrapheap challenge, but I don't think those technically count as crossovers.
Those were the ones that actually had something written down for them, I remember considering a Dr Who/Primeval at one point.
And now I have just realised the potential for a Matrix/Thunderbirds cross. Aw crap.
Hobby writer, here's my sci-fi;
https://www.royalroad.com/fiction/36579/endeavour