Eventually this post will be linked on the front page of the main game community. When it scrolls off the front page, it will still be easily reached. I intend to update it periodically as new NPCs are introduced into the game. Each new NPC will get a comment (complete with icon showing the face of the person "playing" the character), and a link to the main body of the post.
If the NPC is a canon character from a book, tv series, or movies, the medium will be listed in parentheses after the name.
This should go without saying, but just in case it doesn't: If an NPC is a canon character, and you are unfamiliar with the character's personality and history, please don't use them too much. Conversations are fine, but nothing character development-wise or which involves actions and behaviors that might be completely out of character.
Non-Player Characters of Note:
Dees, Maureen Flanagan, Mike Karev, Alex (Grey's Anatomy) Lancaster, Cecelia Mahon, Patrick O'Neill, Jonathan "Jon" (Stargate: SG-1) Thomas, Calvin Torres, Callie (Grey's Anatomy) You are all, of course, invited to add NPCs to the roster as well. Note that this list is intended for "recurring characters" rather than drive-by references to NPCs who may or may not be mentioned again. But if you want to add a comment and describe an NPC, feel free. Feel free also to adopt the icons for any of the NPCs and add them to your user pics so you can use them when/if you post an NPC point of view.