How does my iPod touch knows my location (if it doesn't have a GPS)?

If there's no GPS in the iPod, how can it know (with such a good precision) my location?

GPS uses satellites to triangulate your position with great accuracy, however there are other ways to get a fix provided you can triangulate via other means. Apple uses a database of WIFI networks with known locations to help ascertain your location in some instances (i.e. if you can see WIFI networks A B and E, then you must be approximately located at Z for example). Also, using cellular information you can do a similar thing by noting which cells you are able to see and the relative signal strengths you are receiving from them.

EDIT: Also, it is possible with a lesser degree of accuracy to estimate your location just by using your IP address. This can be tracked down to a certain extent and while likely not sufficient to be accurate by itself, when you combine this with all the other methods above you can start to get a picture with more accuracy.