The startup scene in Rio de Janeiro is growing quickly.  Several accelerators have setup recently in Rio de Janeiro along with angel groups like Gavea Angels which a large interest in stimulating the local startup community.  There are several meetups for people interested in startups in Rio de Janeiro; here is the pick of the litter:

Rio Meetup; meetups every 2 months on Wednesdays at Cafe Del Mar in Copacabana (organized by Tiago Asevedo, costs R$40-70 to get in)

Geeks on Beer; meetups every 2 months in Espaço Lapa
Café in Lapa (organized by Cadu de Castro Alves)

Hora Extra; weekly meetups on Mondays at Informal bar in Leblon (organized by Alexandre Novelo e Vinícius Teles)

DojoRio; a programming event held once a month for coding talent to unite and trade tips.  This is a great place to meet young programming talent.

In terms of annual events:

Startup weekend; a weekend-long startup incubation event that happens once or twice a year.

Startupi has an excellent and complete list of events in the startup community.  Click here for startup meetups in São Paulo.