So I've had a DriveThruRPG account for a long time (apparently to my latest e-mail address, so it can't be that long, I'm surprised I didn't remember it when I tried to create a new one). I recommend it heartily to everyone who has even a slight interest in tabletop gaming. It has tons of free stuff (account is required) as well as other great stuff. Plus, as an added bonus, Classic Traveller is on sale for absolutely nothing (April 7, 2010). So here's a link to it:

Classic Traveller

If you just want to go to DriveThruRPG, a link is available on the side bar.

Oh, one more thing: Check the e-mail invoice from the purchase, it contains links to two additional PDF files that are required to play. It would be nice if they would be more clear about this, but it's still a neat site.

EDIT: You can get Heavy Gear 2nd Edition (and the Technical Manual) and Classic Spycraft, both  of which I highly recommend [though Classic Spycraft will require a d20 player's handbook, there is the "Modern d20 Core Kit" {search that exactly} which is free which can take its place]. Also, there are some nice compiled SRD PDF's.