Psi-Ops, The Suffering, and Area 51 were all made available as free downloads from FilePlanet. As FilePlanet is no longer hosting files, they're available for download for free from places that are Not FilePlanet.
The first hits on google for 'Psi Ops free' and the like seem to be legimate-ish and probably virus/malware free.
The Suffering and Psi-Ops are both still worth playing, if you can embrace PS2 era graphics. I don't think I ever tried Area 51. The Suffering was actually pretty unique in making an interesting, somewhat scary game while still making you an empowered killing machine. It's rather hilarious how many horror setting cliches they managed to cram into one little island as well.
It'd be interesting to see if anyone would bother to put them on Steam and if anyone would buy them since they've basically been abandonware for more than five years now.