Other Games As Resources

[Drachasor]

In the Dresden RPG, Harry asks if he can play a Ghoul/Ninja and Billy says he could. So not as ridiculous as you thought.

It's not as hard as they act like later in the book either.  Just have a decent resource score and you'll be able to buy all the meat you need to eat easily.  (To stick to the ghoul ninja thing for a bit).

[EmirikolTheChaotic]

Ars Magica is an excellent source of inspiration for Wizard characters. Things like the Form and Effect bonus tables would be a great source for ideas on creating enchanted and focus items.

Ars Magica supplements, such as 'The Mysteries' would be awesome sources to draw from to create secret societies, as well as interesting magical traditions.

Also, the Faeries supplement has a huge amount of information that would easily be compatible with the Dresdenverse Fae.

[Janus Node]

I'm a serious tabletop RPG junkie, so here's some of the games that will likely be influencing my upcoming game;

• Fireborn - A game where you get to play reincarnated dragons in a modern world re-awakening to magic.  The dragons in this system are incredibly complex beings, with many established concepts challenged in the genre with new twists.  What I May Use - There are a number of beasties that I loved in this universe that I will look into converting over, and a number of the Sire Dragons make for some interesting Dresdenverse dragons.
• Shadowrun - The classic genre mixing game of Mystic Fantasy meets Cyberpunk, and a world also where magic and tech do not get to mix with each other.  What I May Use - I have always liked the Essence system for the game (the limit of how far a human can be enhanced with tech implants vs. magical integrity) which might help me with my negative refresh house rules.  I also love how creatures in the world have mutated into mythical critters, giving me yet another source for a bestiary.
• (Original) World of Darkness - Dark Modern Fantasy RPG where players get to be the things that go bump in the night.  What I May Use - I want to make a modified scale of roleplay traits based on negative refresh similar to the various "Humanity" scales in the different games.
• Grimm - Children get lured into a magical dimension where the fairy tales of old have been trapped and become twisted with the ages.  A great game for fans of dice lite RPing.  What I May Use - An extensive and creative spell list, as well as learned abilities that might make for some good inspiration for Stunts.
• Call of Cthulhu - I doubt I need to even explain this title... What I May Use - The Great Old Ones.  Seriously, I love these beings as antagonists, especially since they do not need to follow the same reasoning or causality as beings of this world.