Indie Game: The Movie was very interesting and inspiring indeed. Also I would say games like
Castlevania 3 (Basically only you and your whip, memorable and hard bosses, challenging in general, would say it is a platformer strategy game) Doom (simple action, but not too simple)
Contra (challenging 2d tactical action made well)
original X-Com (good balance of stragedy and management, would say Xenonauts took maybe a bit too much away of the management side)
Mario games (basically source of almost all platformer mechanics ideas)
Diablo 1 and 2 (Story and atmosphere. Also character building at least as important as loot)
Dark Souls (No hand helding or even shoulder to cry on. Challenges seem impossible at first. Also interesting story telling)
Unreal (I think it is a
adventure FPS in interesting world. Also the AI was quite unreal at the time)
Startropics (Game keeps you constantly on your toes by introducing new things and traps)
Tales of Phantasia (Something new to old JRPG battle system. Also good music)
Morrowind (First openworld rpg I have played. It was just the thing what I was hoping when it came out)
Rune (very long adventure with good combat)
Severance - Blade of Darkness (More in-depth combat)
Minecraft (Specially the technic pack part would make exellent game. Loads of clones and I don't know anyone to realize this. It was lots of fun to build and design automated harvester/planting machine)
Hexen (Someday I will make that Hexen, Quake, Diablo, Chivalry action RPG with multiplayer and dungeon editors )
Chivalry (Above)
Dust: An Elysian Tail (Nice to look, I would really like this If there would be less fur and enemy juggling. Only one man (:\P )
Insanity's Blade and Dethlands (I also would like to try this type of gameplay again)