I'm ludicrously fluent in English (meaning my B.A. is in it) and conversationally fluent in Spanish (which helped when I found myself alone in Chiapas for several hours and had to find my way back to my group's hotel).
Coming from a classical vocal background, I've grown to love how Latin, Italian, Russian, Finnish, Slovenian, and Japanese flow off the tongue, so I think it would be fun to learn one or more of them.
I've also grown to hate the way French ties my tongue in knots, and grown to be quite annoyed with the way much of German leaves me feeling the need to hack a loogie.