Other than Nighstalker, he's most recently completed a sci-fi film called The Sleeper, which was released last year (2005). He also appeared in X2 (X-Men 2) in 2003. Here's the bio-page for Cotter over at IMDb:
And here's the information page at IMDb for the movie The Sleeper:
Sounds like Cotter tends towards sci-fi film roles, but he's also done quite a bit of TV work, most of which are not sci-fi related. Of note, he had re-occurring roles on Judging Amy, Tru Calling, CourtHouse, and L.A. Law. It mentions, on his bio page, that he did an episode of Thirty-Something back in the 80's. Must be where he met future-wife, Mel Harris (they have since divorced). I think Cotter's version of Anthony Vincenzo is okay but much more hard-nosed than (the late) Simon Oakland's version. But, some would say, Cotter's version fits in better w/ the over-all scheme of this new darker-toned Nightstalker. Perhaps more true-to-life, as well. If new episodes are ever made, I hope Cotter returns to play Vincenzo. Overall, I'd say he's a pretty good actor.