The best competitor research 'tool' is a person who knows how to analyze the data properly. Having data for data's sake is a waste of time.
If you want to learn how to analyze data about your competitors better visit Avinash Kaushik's blog http://www.kaushik.net/avinash/, buy his two web analytics books and invest the time in becoming a better data analyst.
Having said that, here are some tools that I like to use that are either free or have free versions.
These tools give general information about your competitors.
Finding Competitor Links:
With these tools you can find out how is linking to competitors, how their link profile is setup (do they have lots of spammy links?) etc.
With these tools you search for competitor names, their product names and general industry terms to see how they are viewed by people.
With a survey tool run a survey and ask people how they see you versus their competitors. You would need to learn how to create a proper survey.
The success a company will get with these tools is determined by the people using them, so you should invest most of your time in learning what to research and why.