I'm surprised that no one mentioned the possibility of doing a Stargate - Trek crossover. Although the Stargates by itself would be something similar like the Iconian Gateways. I thought one could use them to bring ships or expiditions to another part of the Galaxy, not reachable by Starship, at least not easily or timely.
As I have no seen many episodes of the series and even fewer of SG - Atlantis (is it any good, anyway?!) I could'nt pull someting like this off, as my players most likely would have seen more SG-1 Episodes than me...