SpaceX Dragon is the only vehicle currently flying that has significant downmass capability. European ATV, Japanese HTV, Russian Progress and Orbitak ATK's Cygnus all have destructive reentry, meaning after they are unloaded at the station, they are filled with junk and disintegrate, burn up and sink in the Pacific.
You can take stuff back from the station in the Soyuz when it lands with returning crew, but space and mass are very limited. For example, Soyuz can't bring back the -80°C freezer with blood, saliva and urine samples from the astronauts (those are used, among other things, to calibrate exercise and diet regimens that lead to the least calcium loss from their bones in microgravity).
You can take stuff back from the station in the Soyuz when it lands with returning crew, but space and mass are very limited. For example, Soyuz can't bring back the -80°C freezer with blood, saliva and urine samples from the astronauts (those are used, among other things, to calibrate exercise and diet regimens that lead to the least calcium loss from their bones in microgravity).