IEEE consultant surveys indicated ~$150/hr for a well trained consultant in software is median last time I checked. But what you get depends on how you get your business and what your approach is to selling your services.

I think I'd find it impossible to charge more than $200/hr for embedded firmware (Boston), but could probably get $400/hr for systems engineering or industrial design to develop an integrated complex solution to a business problem that they don't have the in-house expertise to deal with.