La Music Notturna Delle Strade De Madrid No. 6, Op. 30, from the Master and Commander soundtrack. It's composed by Luigi Boccherini. Not sure who is performing it though. I think this is a pretty well known piece, but then again what do I know? Not a lot, when it comes to classical music. I listen to a lot of soundtracks at work though, and this one has really been growing on me. I think it really picks up and gets interesting, aurally speaking, around the 4:00 minute mark. And then again around the 6:00 minute mark. The rest is really beautiful too, obviously. Plus the whole thing is almost ten minutes long, which really helps pass the time while working.