Well, since E made provided a log, I thought I'd put one together too. Here's our travel log so far this year:
DC
Maryland
Virginia
Florida (airport only)
Puerto Rico (including the separate island of Vieques)
New York (airport only)
West Virginia
Pennsylvania
Ohio
Utah (E and Cadie)
Delaware (E and Cadie)
Vermont (Eric)
Colorado
Germany
The Netherlands
Belgium

My favorite place is Maastricht in the Netherlands, although the Rhine Valley was pretty impressive too.