One of my favourite districts along with Trastevere. I think the reason that I like it so much is because it has a French feel to it. In the centre if the district there is a lovely square with a fountain in the middle. Behind the fountain is a really cute cafe / restaurant, where there is seating under a canopy of leaves. If you go during the afternoon (and not during Aperitivo time) you can get a drink with a couple of light shacks such as small pieces of croissants filled with parma ham as well as the usual nuts and crisps (wine starts at €4).
See 'A Perfect Sunday' to read more about it.