Shadow complex is one of the interesting exceptions, and one of all of about 3. Technically an older version of the game could bypass the end of demo wall and thus allow you to play the entire game, I am not sure if that version has since been blacklisted but it was quite hard to find when I went looking a couple of years ago.
The only thing you can do is download the demos and play them. All the other methods (profile sharing, COD glitch and live2con*) have long since been blocked. To play downloaded XBLA titles you need a JTAG or RGH modded machine, there is some DLC you can install safely on unmodded consoles that came with various game of the year type games. It is called PIRS DLC and there is not much of it but what there is happens to be worth taking note of (some of the borderlands expansions, some fallout 3 stuff, some oblivion stuff, some mass effcect stuff and a few other notable things; it tended to be from games that thought they warranted a game of the year edition so they tended to be notable games), it is still paid for content though so I can not link it up here.
*there may still be some things out there possible with live2con, XBLA and worthwhile DLC are not part of it though.