Well there are several good spots in the USA.
Obviously, APG has been the "Holy Grail", but it is a case of good news and bad news. As mentioned, the collection was allowed to deteriorate, which was criminal as they have many unique items. Good news is that there have been efforts to get some stuff repaired and painted. A slow process, but at least it's started. There have been stories about moving the Museum to Ft.Lee, VA as part of a base realignment program. I haven't kept up on the status of a possible move.
The BEST single government armor museum (IMHO) is the Patton Museum at Ft. Knox. Their acquisition and restoration have been going longer than APG's. The problem with Ft. Knox is that about half of the vehicles are in storage, only part of the collection is readily available to the public. They do have some "runners" that they fire up about Memorial Day weekend and also on the 4th of July. They have mock battles between German and American forces. A number of nice displays inside the museum and a friendly staff.
The Military Vehicle Technology Foundation is the collection of Jaques Littlefield. Unfortunately, being a private collection with a lot of active restoration going on they are VERY limited on tours. Many of the vehicles have been meticulously restored. There has been a friendly rivalry between the MVTF and the Wheatfield Collection, a private collection in England, to see who gets their Panther fully restored first.
There are several other small museums and private collections including the 45th Division Museum in Oklahoma City, OK, the 1st Division Museum near Chicago, the WW2 Victory Museum at Auburn, IN, and the military museum at Hubbard, OH (which will host the 2008 annual meet of the Armor Modeling and Preservation Society), the Heartland Military Vehicle Museum at Lexington, NE, plus others.
It all depends on your time, your interest and where you are starting from.
Have a good vacation,
Gary
