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.
Set 2: Rules/setting integration. The Storyteller System would be revisited for this one, with examples such as the Humanity rating and the Virtues. Then we'd add Blue Planet, 7th Sea, and Call of Cthulhu.
- Blue Planet: The damage system in this game is a great example of using scientific knowledge to influence gaming. This meshes excellently with the great levels of hard science evident in the design of the game world, from plausible slower-than-light space travel to a believable alien planet.
- 7th Sea: This game sets out to enable players to experience epic swashbuckling adventure, likening the stories told with this system to the greatest adventure films. To this end, they use an innovative mechanic: there are varieties of antagonists. It's been years since I've played, and I don't remember the system very well, but I do remember that most of the enemies you fight only had one 'hit point.' If you do them any damage at all, they fall unconscious. This emulated the ridiculous ease with which cinematic heroes would easily defeat hordes of foes.
- Call of Cthulhu: This game was based on H. P. Lovecraft's tales of things man was not meant to know. As such, it introduced the Sanity Points. Certain events, including casting magic spells, caused you to lose Sanity Points. An early example of creating a rules system to replicate an important part of the setting.
- Toon: A low-budget, not-very-high-production scale game. The layout is simple, the artwork bland and sparse, done in black-and-white line drawings.
- Hol: Moderate budget. The drawings are still black-and-white line, but they're a much higher quality. Also, the text is completely handwritten, and changes style depending on what the authors are saying (at one point, for example, the authors get angry, and the text becomes large and irregular).
- Exalted: Very high budget. Lavish colour illustrations, high-quality paper, hardback covers, the works.