DSM and DTM
A Digital Surface Model (DSM) shows the elevation of the earth surface inclusive what on it (e.g. inclusive trees and buildings).
A Digital Terrain Model (DTM) shows the elevation of the earth surface of the bare soil, so trees and buildings are stripped off.
NextMap Elevation products (from Intermap)
NextMap Elevation products from Intermap are available as DSM as well as DTM. Grid cells can go down to 5x5m with a Z-accuracy of10m (LE90). A global coverage is available with 10x10m and 10m vertical accuracy (LE95).
WorldDEM products (from Airbus)
WorldDEM Elevation products have grid cells of 12 x 12m with a vertical accuracy of 4m (LE90).
Vricon DSM (from Vricon Saab/Digital Globe)
Vricon Elevation products are the most detailed and accurate available. The unbeated 0.5 x 0.5m grid cells with a vertical accuracy of 3m (LE90).
AW3D Elevation (from JAXA/Restec)
AW3D elevation products have grid cells of 5 x 5m with a vertical accuracy of 5m (LE90).
SRTM (Open accessible)
SRTM elevation products have grid cells of 30x30m and have a vertical accuracy of 10m (RMS). Elevation info is from the year 2000 and up to 60 degrees north and south only.