I think you read me backwards. What I meant was that stackoverflow (and all the other stacks) are missing, and I find Quora seriously lacking, so the fact that it is on there at all makes me question the quality bar for the entire list.
thx. Stackoverflow added.
I've tried several of the wireframing tools you list, and I prefer Mockflow (http://mockflow.com) to them all.
Thanks!
We find all of the following useful:
Billing:
http://FeeFighters.com helps find a credit card processor and reverse-auctions down the rate