Traveller: The best developed Space Opera of all. With incredible detail and flexibility combined with a rich setting to serve as it's base. There is none to compare with it. And I do mean none.
Infinity: The most dynamic rules, best cyberpunk models in the market AND it gives out the rules for free? YES, please!
Warhammer 40,000 is completely awesome for extremely obvious reasons.
Exalted runs on Rule Of Cool in a Fantasy Kitchen Sink world. Your characters range from archetypal heroes to supermen akin to benders, from shapeshifting barbarian death-machines to fate-ninjas. The system itself rewards players for coming up with outlandish, heroic action with bonus dice.
Exalted creates a Fantasy Kitchen Sink world where absolutely everything has been turned Up to Eleven for maximum awesomeness, then has excellent writers lovingly tie all the disparate ends together, until you find yourself pondering the geopolitical ramifications of demon pirates battling ghostly ships crewed by zombies on the western oceans.
Or even better, it's Spiritual SuccessorPathFinder. Awesome redesigns of classic and often ridiculed monsters. Epic new additions. And... You know I could talk on and on for hours.
In Nomine desperately Needs More Love, the system is quirky but simple, and the setting will EAT YOUR BRAIN (in a really awesome, good way). It can be played in so many different ways from dark to light and happy to satirical, to just plain silly depending on your preferences. And just to add icing on the cake, it would likely tick off any religious fundamentalists that found out about it, due to it's let's say... non-traditional treatment of angels, demons, and theology.
Lesser Shades of Evil is awesome; it is science-fiction but somehow it feels completely like fantasy, and makes you think about themes like sin and evil, free will and freedom in general, Grey and Gray Morality... like you wouldn't believe it. It also deconstructs thoroughly classic fantasy tropes like the Evil Overlord. More people should know this gem.
