Whether it's French, Spanish, or Japanese, we're very interested in raising our kid to speak or at least understand a language besides English.
This weekend in the park, we happened to meet three French/English families, which'll get me off my butt to research good techniques and resources. Stay tuned, and feel free to add your dos centavos below.
But in the mean time, I found one second language that, 999 times out of 1,000, your kid will thank you later for avoiding: Klingon. [As a 9th or 10th language, if you are a professional TrekCon promoter, maybe.]
A new documentary, Earthlings: Ugly Bags of Mostly Water, includes interviews with members of the Klingon Language Institute, including Dr d'Armond Speers, "a linguist who spoke only in Klingon to his son until age three and a half." [emphasis added to register utter shock and disbelief. via boingboing]