I don't know if I still have them with me anywhere, but one of them was the demo for Metal Gear Solid 1. It got to as far as until you met with the DARPA Chief before it ended. Despite that and thankfully due to the PS2 backwards compatibility, I played that demo so much when I was young, it was the reason I got into the MGS franchise, albeit, mostly watching longplays of the series back in 2009 if I recall. Totally all worth it. XXD
Seriously wish that PS1 stuck around well into my younger years, there was so much I missed there, it's kind of amazing. --w--
The only other game I remember playing super frequently via PS2 Disc Backwards compatibility was this driving, shooter game called "Auto Destruct". It was a simple game where you had to drive around, seeking targets to destroy to accomplish goals, with a few time based missions, chasing missions, etc. Three different "worlds" which included San Francisco, New York City, and Tokyo, all in that lovely nostalgic dithering graphics that we all come to love when it comes to anything from the PS1. ::B

OH, and there was also the disc for Crash Bandicoot: Warped!...Problem is the game had a chunk missing in one area, and yet it ran pretty fine...Then it proceeded to get stuck in my PS3 and spent a whole day getting that out of the tray. ..w..;;;;;;;;;