Here's the best open data source for trend data I could think of: Wikipedia page view statistics. Derived datasets:
Wikitrends, a daily/weekly/monthly updated list of 10 most popular (as in page views) articles. Bonus: not only absolute, but also relative change top 10 lists (called uptrends/downtrends) are offered.
Wikpedia:5000, a weekly updated list of ...
I considered crawling twitter hashtags, or facebook hashtags or google trends, but the thing is people use many useless keywords and hashtags nowadays like #I_ate_pizza #I_love_bieber and they don't search for keywords, the majority search What gift to buy for my girlfriend
I don't really know Facebook, but regarding the Twitter trends:
I've just been playing with Socrata's site metrics. You get a quite a lot of information, which is nice. Unfortunately, Socrata doesn't have very many users, and its users are probably quite strange compared to the rest of the world.
While I don't work for The Post or Google, and thus cannot speak authoritatively, I was at a Google event for top news organizations last year in NYC, and can attest to the fact that -- depending on the publication -- Google often provides custom Trends data as an enterprise service to publishers. That would be my guess here.
note: this answer is based on another answer, with some modifications for your question.
Google Trends doesn't have an API, but you can follow instructions from this great blog post to hack it. The raw data is in JSON form here:
and using this curl command you can change date and region:
curl --data "ajax=1&...