Big mouth talk a lot. (sorry couldnt resist)
The only company that ever impressed me was GreenLight, and they have a minimum spend of £10,000 so most of the time its severe overkill.
Im also not sure about the techniques they use anymore.
Most of the info you can get off forums or do yourself.
However a trick you can do, is hire a company to manage your ppc for a month or two then check your referre tracking, see what terms they are bringing in traffic for, whats converting, etc. Then do it yourself after they have done the keyword research.
