Here's the themes (Enredos) of each of the 12 samba schools parading in the top group of Rio carnival 2011, on the Sunday and Monday nights of carnaval. The Carnavalesco is the overall designer of the parade. Each school parades with around 4000 costumed participants and 8 large floats. The parade is divided into sections with costumes and floats illustrating aspects of the theme. Each school has its own song (samba enredo) written specially to explore the school's theme.
A few months ago I posted up a link to video of some of the samba schools in Rio carnival's lower leagues. Some much better quality video is now beginning to appear on youtube.
These schools are parading in Intendente Margalhes, a street miles away from the Sambodromo. They have very few resources and little cash to stage their desfile but I find these Samba school parades extremely impressive, and also rather moving. Also certainly not little by any normal standards, just small compared to the super - escolas of the top leagues. They parade on the same night as the big, famous samba schools over in the Sambodromo, but I think I prefer these.
One day I hope to be able to go to Intendente Margalhes and watch these unsung jewels of carnival, live.