C'mon, PS2 games? Really? Those are hardly 'old'.
The original Sonic series, the Capcom/Disney games (except for The Jungle Book. Blech.), Lemmings, you could check out the Back to the Future ones, too. I only have the third (wonderfully terrible), but the others would probably be fun, too. Lots of ones for the SNES/NES, the Atari 2600 is pretty cool, the N64 is always a favorite, the list could literaly go on for miles.
And, though not yet fully considered old, the GameCube has tons of games that would be good for walkthroughs. Just saying.
Should you decide to really write some, post the link. Free online walkthroughs are wayyy better than ones for twenty bucks that you'll only need once. 'Cause once you beat something the first time, it's kinda committed to memory, right? Or is that just me?