First, GREAT thread idea [MENTION=93390]smoelf[/MENTION]!
Considering world-building is one of my favorite aspects of the RPG (specifically D&D/fantasy worlds) and comparative religion and mythology is something of a lifelong interest of mine, theology and philosophy are significant elements for generating a rounded and rich world/nation/culture...or even single region or encounter.
I encorporate a great deal of theology in my gameworld...In all honesty, I could do more/better with the strictly "philosophy" elements. My default is to take certain beliefs and views and wrap them into a religion of one of my world's gods. But the idea of a "philosopher", outside of religion, is an intriguing one that could see lending to all kinds of color and flavor for a world.
Though I've not done it myself, I have heard of GMs creating worlds that do not possess "religion" per se, but instead various schools of thought...The "clerics" of these types of worlds ARE the philosophers...their level of "enlightenment" (which, naturally increases as the levels of experience increase) is the source of their spells/powers. While I've never played a world liek this myself, I find the concept very interesting and potentially great fun.
Some elvin ethnicities on my own gameworld are, in fact, immortal...other "lesser elves" are not. What plays to other races as "arrogance" or "aloofness" is really simply a societal sympathy or, more likely, pity, for the mortal races and their (as far as the immortal elves are concerned) "shortcomings" due to their "limited existence."
I also, assign for all nations (or any race) a general Alignment (using the "old"/original 9-point alignment system). This, naturally, involves (or "evolves", if you prefer) over time so that cultures and the races within it have shifts of alignment as to what is "acceptable" behavior and concepts. As a brief example, the original race of elves (yes, who are immortal) began their existence as the greatest force of "good" on the continent...yet, in the millenia that have passed since the birth of the race, they are -as asociety, mind you- passed into decided Neutrality...Lawful Neutrality, but neutrality nonetheless.
Centuries of watching the races come and go, the nations rise and fall, they led to them sequestering themselves over a thousand years ago to avoid "corrupting influences" of other "limited" (read as, "mortal") peoples and their, from the elves' perspective, "momentary" problems.
They despise intrusion or influence from other cultures. Their society has stagnated...simply because they have reached their pinnacle and have, literally, all of the time in the world.
For theology, I have (or rather, what I think is) a diverse/flavorful pantheon. The gods ARE real, but due to the near-destruction of the world by their forebarers, the "king of the gods" has decreed that the current pantheon "keep their distance", working through their representatives (various temples, clerics and paladins) by granting visions and powers (spells) but not "directly" effecting what goes on in the mortal realms...and "manifesting" themselves in mortal is forbidden to all but a few lesser deities.
Naturally, the "evil" gods are not so compliant with this decree...though most are content to send representatives or chosen avatars to conduct their sinister business.
Druidism in my gameworld is, I suppose technically, a "religion"...the most ancient remaining on the world, in fact. But it really is more of a philosophy of communion with nature, as there is no druidic "god"...they join/commune/grow with the energies of the world itself. Druids are viewed as "heathens" is not outright "blasphemers" (depending on the established religion) by temples of the gods.
Hence, there are sometimes certain....differences...of philosophy and points of view with priests of "the nature goddess of Men" (the actual goddess of nature and weather in the pantheon) as well as significant differences/troubles arousing from those deities that handle domains at odds with maintaining "the Balance" of the natural world...things like "Law" or "Civilization" or the over-culling of resources.
But yeah, great topic and interesting responses thus far. I look forward to seeing much more.
--Steel Dragons