Ask HN: Open Location APIs

These days there is a lot of talk about location (4sq, FB places, etc). I am curious which services out there have open APIs that one can use to create mashups (and just generally query).

I ran across an old HN article -- http://news.ycombinator.com/item?id=216112 -- which is an interesting start, but being over 2 years old is a little dated.

I guess my question is simply -- what services out there allow location based queries to their data, what rates/limits do they put on them, and are there ways to getting greater access (for instance w/ Twitter -- the firehose vs. normal account query limits).

If there is already a good list, please share that. If there are some hidden gems, I'd love to hear those too.