I am overwhelmed by the variety of types of satellite and aerial data (images?) available online. For example, at the USGS Earth Explorer data page, I see AVHRR; CEOS;Ikonos and OrbView; EO-1; GLS; HCMM; LPDACC (which contains AirMOSS, ASTER, MODIS, SRTM, ...)
At different times, I am seeking data for different purposes. Sometimes I want clear, high-resolution images; other times it may be something else.
Is there a good guide to the aerial and satellite data products available for download? I would like to read about what data types are good for what mapping purposes, and then see references to tutorials or instructions on how to process/use the specific data type.
I use QGIS.