OED Online Word of the Day
When I was in college, I took a cool course about the etymology of words. It touched a great interest I had, and has resulted in me having all sorts of books about word history, the origin of words and phrases, you name it.
You can sign up to receive a daily Word of the Day from the Oxford English Dictionary. (Check out The Professor and the Madman by Simon Winchester to learn about the history of the dictionary; I got it as a great birthday present and really enjoyed it.) Each morning (relative to your timezone) you’ll get a new word with its complete OED entry, including pronunciation, etymology, definition, and the variety of specific texts that used the word over the last 500+ years. They’re amazing, ranging from swelling to the more recent addition of D’oh.