We selected Americas Mailbox in Box Elder, SD. We kept track of mail for about 6 months to know with whom we needed to change address. We believe we were able to give our new address to all the important contacts. (Update: Well almost, we forgot the old water company. They called finally called before giving our final bill to the collection agency. But otherwise we done good.)
After capturing all the important mail we changed addresses for these. We then did not put a forward from our old address, this should stop all the catalogs and other junk mail previously received. We'll send out a note to our Christmas card list indicating no mailing address, then send a Christmas letter via email.