You can use GID both for preprocessing (mesh generation) and postprocessing (plotting). An extension of GID is available by the name Tochnog-GID, see the homepage. The use of GID is recommended.
With gnuplot you can plot files resulting from control_print_history and control_print_data_versus_data. Also any other x-y plotting program can be used for such files.
Some other plotting programs can be also be used; see the control_print_* records.
See the links sections at our homepage where to get these programs.