Kevin Williamson has a great column today about science fiction dystopias that are run by corporations. As he observes, this is a very unlikely outcome.
Fact is that corporations have only been oppressive when they get government help, particularly state guaranteed monopoly power. The classic examples of this are the British East India Company and the Dutch East India Company, both of whom became de facto colonial governments with their home county governments’ assistance.
Thankfully, there are a lot of competing science fiction visions that take a much more libertarian bent. For example, "Cryptonomicon" by Neal Stephenson and the LaNague/KYFHO series of stories by F. Paul Wilson are both anti government and fun to boot. Try them as an antidote to corporate villains.