Google Lab's new Search by Location service lets you aggregate results for hotspots: This is nifty idea which aggregates the address information that Google is parsing from its results (any time it sees anything that looks like an address) and tying it to keywords.
It's particularly useful for Wi-Fi aggregation, because you're finding locations that not only my business partner JiWire lists or libraries that Bill Drew has assembled, but you're seeing even individual locations like coffeeshops that mention they have Wi-Fi, community wireless pages, and other randomly related content.
I've pumped in my office Zip code in the link above, but try other combinations.
Note that JiWire's listings are prominent because of how they structured their site. As a group of former Cnet.com'ers, they know that if you expose URLs that are permanent and look like "good" URLs (not full of argument junk after a question mark) then search engines will well index their hierarchy. This is hardly a secret, but many sites still haven't discovered it. [link via Jim Thompson, Doc Searls]