If you want to be an FBI agent that gets the good postings I would get a law degree from a top school and graduate with honors. That way if it does work out you have something to fall back on. Any of the other agencies would consider a lawyer from a top school or you could just practice law. Another good agency you might like is the US Marshals' Service which I think isn't quite so degree oriented but still finds and trains good people who can be in the thick of amazing things.