Ask HN: Recommended language to learn data manipulation

I have a few very large datasets (in csv format) that I need to work with that completely overwhelm Excel. I'm looking for recommendations on a single language (or minimal number of languages) that I could learn in order to take these datasets in and start running various calculations on.

Simplicity and future usefulness of the programming environment I'll be learning are my highest ranked criteria.

I'm not necessarily looking for a how-to book (though I wouldn't turn it down) I'm really just looking for language advice. There's a lot out there on the Internet, and much of the advice is conflicting.