The USGS archive holds data collected by the Landsat suite of satellites, beginning with Landsat 1 in 1972. All Landsat scenes in the USGS EROS archive are available for download at no charge. The Search and Download page describes how to find Landsat data.
The USGS Landsat Global Archive provides a graphic view of the acquisition of Landsat data from 1972 to 2012.
Currently, both Landsat 8 and Landsat 7 collect data, following a near-polar, sun-synchronous orbit on the Worldwide Reference System (WRS-2).
The Landsat Acquisition page lists daily capture schedules, acquisition calendars, and pending acquisitions.
Landsat 8 collects more than 400 scenes per day, with data downlinked to the USGS Landsat Ground Station becoming available within 24 hours of acquisition, on EarthExplorer, GloVis, or the LandsatLook Viewer.
Landsat 7 collects about 300 scenes per day and scenes downlinked to the USGS Landsat Ground Station becoming available within 24 hours of acquisition, on EarthExplorer, GloVis, or the LandsatLook Viewer.
Landsat 5 has orbited Earth over 150,000 times since it was launched in 1984, making it the longest-operating Earth observing satellite of its kind. Acquisitions were ceased in 2012. The latest details about Landsat 5 can be found at http://www.usgs.gov/newsroom/article.asp?ID=3231#.UGCu4vU-c7x.