I've noticed a wonderful trend in AAA (big-budget) games lately: many of them include DVD-style bonus content as unlockables. This includes reference art, developer interviews, and other behind-the-scenes stuff that really gives some insight into the game development process.
These things are great for the classroom. All of the stuff I'm teaching about the theory of how games are made, is reinforced by live developers that made a really sweet game. Some of these developers are important enough that a student should know what they look like in case they meet them at GDC or something.
So far I've found three games in my personal collection with this kind of bonus content:
God of War
Sid Meier's Pirates! (Xbox version)
Unfortunately, in all three games, I actually had to play for a bit to unlock these things. But that's the kind of selfless sacrifice I'm willing to make for my students :-)
Have you encountered any other games lately that feature this kind of material? Please let me know!