In terms of in-country travel for Infidels, there are bound to be problems with the United States. Certainly, if you wish to avoid being intellectually offended, you may also wish to avoid the Bible Belt, with its preponderance of Christian Fundamentalists. This will hopefully begin to change after the 2006 elections. On the other hand, you may enjoy confontation and thus might love pursuing such a vacation as a Secularist Commando.
The Northeastern region of the country is slightly more Infidel-Friendly. It was, after all, this region that was primarily responsible for the Separation of Church and State embodied in the Constitution of the United States. It still seems to be doing a god job of resisting the revisionist history relative to Church State separation being pandered about by the religious left; no matter what they try to tell you, this was not intended by our forefathers to be a Christian nation.
To this end, you may wish to try a few days in Boston or Concord, especially in the fall. Enjoy a walk through the history of our American Freedoms while they are still around; politicians controlled by the religious left are doing their level best to take all of those freedoms away from us. If they succeed, you may be sure that the historical record will be wiped clean.
Washington D.C. should be avoided during the sultry summer and also during Fundamentalist Lobbyist Season, which is whenever our legislative bodies are in session. This coincides with the Big Business Lobbyist Season. If you have to go during these seasons, always be ready to scamper out of the way of the politicians scampering to the Fundanentalist and Big Business feeding troughs.
The American West may still offer some interesting vacation possibilities in the United States. San Francisco is still as raucous and diverse as ever. Much of Arizona and New Mexico have thus far avoided much of the religious fervor that has affected other parts of America that occupy their latitudes. And there is always the great Northwest, including Seattle and Portland, and the entire State of Alaska.