The Wireless Node Database Project currently lists 3400 public and commercial WiFi access points, mostly in the US.
UPDATE: An affiliated site, LocFinder.org lists over 7800 WiFi nodes, which it claims is the largest directory anywhere.
I gave a talk yesterday to US state regulatory commissioners on unlicensed wireless. Unbenknownst to me, the program billed it as, "broadband wireless demo." So I pulled out my laptop, snapped in the WiFi card, and sure enough, it picked up an access point. It was apparently a private network rather than one offered by the hotel, but still, I was able to show what organic connectivity means.