The American Gut Project is an open-access microbiome project run through the Knight lab at the University of California, San Diego. The project itself is part of the much larger Earth Microbiome Project which is an international effort involving over 100 labs world wide.
It is possible to send the American Gut Project a sample and look see a summary of the organisms living in the gut using genetic sequencing of the bacteria. The American Gut is based in the United States but it is not restricted to US participants. In addition to the American Gut, there is also a sister project in the UK called the British Gut Project (run by Tim Spector who wrote The Diet Myth) that uses the same online back-end. An aggregation site is also run in Australia through the Australian Centre for Ecogenomics at the University of Queensland which greatly reduces postal costs for participants from that part of the world.
At the time of writing the reports produced by uBiome appear more extensive but the methods are not assured to be supported by the scientific literature.