Hm. Suppose it depends on what you like. I revise by having something related to what I'm doing. So, for Spanish, I put on a lot of Spanish pop (Shakira, Enrique Iglesias, La Casa Azul etc) and latin folk stuff; for Italian, it's mainly Italian folk; for history, it's classical.
I'd say go for classical or post-rock - something without words, unless you're doing a language, in which case find something with lyrics in that language. As for classical recommendations - Joaquin Rodrigo's Adagio from Concierto de Aranjuez is my all-time fave; then I branch into Saint-Saens, Greig, and Bach. If I'm in a particularly foul mood, I'll put on Wagner in the background...