I started thinking about this, and here's what I've come up with. I think the best way for what I have in mind is to have three groups of three: the first to cover different rules systems, the next to cover rules/setting integration, and the last to cover artwork/production. There will be some overlap.
With that in mind, we start with group one: rules systems. The three games I've chosen for this set are Dungeons and Dragons, GURPS, and the original Storyteller System.
- Dungeons and Dragons: An example of level-based systems. Really, any edition would work equally well for this, although I think 3.5 is probably the easiest for new players to learn. Alternately, you could use almost any d20 system game, like the Farscape RPG or the d20 Star Wars. Another advantage of 3.5 is that it is a good example of the 'attribute+dice' style of game system.
- GURPS: An example of points-based system. It also demonstrates the possibility of creating a 'realistic' game system, rather than the epic style represented by D&D. Also, of course, a perfect example of a universal system. A perfect example of the 'attribute vs. dice' style of game system.
- Original Storyteller System: An example of a non-points skill-based system. Also an example of how rules can encourage players to focus on character and plot, rather than combat. Good demonstration of how a core system can be modified slightly to accomodate different settings without requiring a universal system, but still allowing crossover between different games. Finally, an example of the 'attributes=dice' style of game system.