Delta Green
Looks like everyone has pretty much described what Delta Green is, so I'll just add that I'm Von's friend who talked the poor folks of the local gaming club into playing in my game.
Also, when I got Spycraft and d20 CoC, I immediatly thought, "Cool! I can do Delta Green in d20 now." VorpalBunny's right: that was a mistake. Spycraft characters are supposed to be bad-asses, and don't fit that well in Delta Green. A friend's 6th level Hacker could've broken into the Majestic 12's mainframe, in real time, just by taking 10. My Pointman/Faceman Navy lawyer could've appropiated enough equipment, resources, gadget points, and troops to turn a Shoggoth into fruit jell-o.
So now that d20 Modern is out, use that instead. It's a little more cinematic and action-driven than normal Call of Cthulu, but then again, Delta Green allowed for a few more shootouts, chases, and firepower. I know I'll probably get slammed for not using straight CoC rules, but considering that the group I'm running with haven't played the original setting and rules, I have to be gentle with them

So far, it's been going great. Even with high stats, training, and the d20 Modern talents and abilities, the agents are still having trouble and their SAN is going down the drain...
Delta Green: Countdown is also great. And I also think it's better, but only because it supplements the original. While Delta Green focused more on the US, DG: Countdown goes worldwide. Imagine the British Intelligence agencies subverted by Mythos creatures. The Russians are fighting a holding action against Ghouls, while being destroyed from within...And my favorite part of all: it the Outlook Group and Hastur Mythos...
And here's another DG link:
http://www.semper-vigilus.tk/
So watch the skies and be seeing you...