Just found an awesome site for locating virtual office services in the United States. Find A Virtual Office (http://www.findavirtualoffice.com) has a great selection of virtual offices in all of the major metro areas around the country. They have virtual office space in US cities like Austin, Dallas, Denver, Boston, DC, NYC and others. The service is super affordable and feature rich with things like a local mailing address (in a high profile location), dedicated phone number with live receptionist, fax reception and more. They also offer conference room space for rent as needed. This is huge for anyone that has tackled the issue of where to meet a client for a meeting when you work from home.
If you aren't familiar with virtual offices or what they can do for a business you should check out this brief video. It is very informative.