A complicated question, on some levels.

Imperatriz’ samba enredo has been voted the most popular of the Grupo Especial songs for Rio Carnival by a specially selected panel of judges in O Dia, the Rio de Janeiro newspaper. I agree; nice melody, good lyrics and, crucially, easy to sing.
Imperatriz’s theme for carnival 2010 is ‘Brazil of all the gods', and you can see a preview of their costumes for carnival 2010 here. Imperatriz’s carnavalesco (artistic designer) is Max Lopez. The official Grupo Especial CD is released on 7th December; you can buy it here.
The pagode do Trem - a samba party till dawn in Rio, involving four sound stages, many samba stars, song, dance, beer, and four trains. Now this is an event that I would REALLY like to experience...
Celebrating the Brazilian Day of Samba on Dec 2nd, the event starts with a live stage set up in Rio's central rain station. From 12pm there's a big samba da roda in the station, with many samba stars performing - including (in 2009) the velha guardas of Mangueira and Portela.
Then, from 7pm, four trains set off towards Oswaldo Cruz. These party (pagode) trains contain a mixture of normal passengers, drums, music, songs and samba stars of the calibre of Nelson Sargento and Dona Ivone Lara. Everyone disembarks at Oswaldo Cruz, where there are three more music stages and a party that goes on till dawn.

I've heard a sneak preview of the Rio carnival official samba CD 2010 (Grupo Especial) and it rocks! Read more here
The Rio samba school Salgueiro is planning to be holding its street rehearsals regularly on Wednesday evenings at Rua Sivas Teles, starting at 9pm.
The whole samba school will be practicing their parade down on the street, and singing their samba for 2010 "Stories without end"
The bateria will be out in force with over 200 drummers, led by Mestre Marcão, and the puxador Quinho singing the song through a huge mobile sound system.
As usual with street rehearsals, there will be hot dog stalls, street barbecues, plenty of beer and other street food and drink to create a real party atmosphere.
If you get the opportunity, here's how to get the very best out of your experience.

You can buy a tourist package for Rio Carnival that includes parading with a Samba School. You can also organise it yourself (advice below). Either way, if you want to know how to get the most out of this once in a lifetime experience, here's how to go about it.

Heres a pic of one of the costumes the samba school Mocidade Independente is producing for carnival 2010.