I liked doing pull ups, but the arms seem to wear some before the lats get a total w/o. The lats are a large group and can take time to build them, so be patient.
Personally, I think rows (standard BB rows if that is all you have) puts mass and thickness on the back.
Also, as Driven^ says, add weight. 20 reps is probably not really building your mass as much as it is just pumping you up or tiring you out. Add weight, do rep ladders etc. etc.
Also free weight stuff...
BB bent rows
Yates rows
T bar rows (stick a bb end in a wall corner and do meadows or something
One armed DB rows
Kroc rows
Heavy deads too
Lots of free weight rowing.
Also, eating enough has a bit to do with mass.