The ACLU’s published a photographer’s cheat sheet on their rights when shooting in the field (US only):
When in public spaces where you are lawfully present you have the right to photograph anything that is in plain view.
When you are on private property, the property owner may set rules about the taking of photographs.
Police officers may not generally confiscate or demand to view your photographs or video without a warrant.
Police may not delete your photographs or video under any circumstances.
Police officers may legitimately order citizens to cease activities that are truly interfering with legitimate law enforcement operations.
Note that the right to photograph does not give you a right to break any other laws.
Click through for explanations of each, advice on what to do if stopped or detained, exceptions for shooting around airports and special considerations for videography (eg., “With regards to videotaping, there is an important legal distinction between a visual photographic record (fully protected) and the audio portion of a videotape, which some states have tried to regulate under state wiretapping laws.”)