For foreigners, my guess would be adrs traded on nyse and nasdaq. For actual bovespa trading, I can recomend a few houses...
Here is a fine list: http://www.halfeld.com.br/guia.htm Way too many to choose from. Agora is the most popular one but expensive. Tov is cheap and you can short stocks, Codepe is R$200/mo and you can trade unlimited shares. All of them have poor trading platforms but oh well it's an evolving biz... I have not tried any of them but been looking into opening an account and have asked friends in the biz that recommended these houses.