What are the big non-d20/non-D&D Game Systems?

[Rechan]

Don't Rest Your Head is getting supplements (They just released "Don't Lose your Mind", for instance). But I wouldn't classify it as "Big". I'd argue that while Spirit of the Century is having a lot of sales, they're not really doing many suppliments.

Now, I'd say Shadowrun would be big if it came to supplement matters.

 

[Particle_Man]

Don't Rest Your Head is getting supplements (They just released "Don't Lose your Mind", for instance).

...

WHAT?

I am so getting that!

 

[Fenes]

Shadowrun's "Unwired" and "Street Magic" are already out, Unwired's PDF is available since the 21st and should hit stores any day now. Street Magic came out in print and PDF last year.

 

[Dr. Strangemonkey]

Weapons of the Gods has at least 2 books out, and is awesome.

Nobilis is only one book, but is most certainly a system.

Neither are particularly big.

Earthdawn deserves a shout out.

As to the Default Adventure Question:

Exalted:
Step 1 - I am a super cool dude or lady. Oh God, Something I can't Deal With.
Step 2 - Hello, I'm the Unconquered Sun - a totally awesome mega-deity - just wanted to let you know you're a demigod now.
Step 3 - Alright, I easily solved my problem with glowing light and unstoppable awesomeness. Now I have to run from an army of elemental super soldiers and their badass kung fu inquisitors. I may also have to dig up some tombs, build some magic palaces, and learn the true names of demons.
Step 4 - Watch as Gem as Destroyed.
Step 5 - Either solve all of the world's problems in a completely over the top way or tragically destroy all of creation. Possible both.

Weapons of the Gods:
Step 1 - I am an earnest disciple of Kung Fu! I'm going to mouth off to someone who will beat the crap out of me shortly.
Step 2 - Why am I in such horrible Pain?
Step 3 - I'm gonna learn more Kung Fu and go on awesome adventures. Also I will learn how to be awesome through feats of virtue.
Step 4 - I solved a mystery!/Got a pair of nunchucks made from the sighs of the first sinner's dissapointment!
Step 5 - I'm gonna take out that guy who beat me.
Step 6+ - What's a Hell Clan and why are they systematicaly killing everyone I love?

Nobilis:
Step 1 - Wait, what? No dice?
Step 2 - Time to read the rules, geearrgghh! My mind! My precious precious neurons!
Step 3 - Now I have a graduate degree and on the weekends I play the avatar of the Napoleanic Code in my constant battles for Dame Justice.