In what state do I register my LLC?

I am starting a consulting firm with my friend who lives in Washington, D.C. but I currently live in Virginia. To make matters a little more interesting, I will also be moving permanently to Pennsylvania within the next 6 months. Although we will not have office space and are able to primarily do our consulting by either visiting potential client sites or over the phone, I assume that once the business is up and running, the majority of our clients will be from Virginia. I am looking for some thoughts/advice or the correct place to go and speak to an expert so we can register our business and do it the right way the first time around.

There are two major factors:

• First, which state is easier and cheaper to organize in, including annual taxes (franchise tax or the equivalent)?
• Second, are there any state specific laws that make one state more attractive than another regarding ownership and organization?

The state of organization and the state in which the business is located don't need to be the same. A lot of large companies are "Delaware Corporations" because it used to be (and may still be) advantageous to register there.