I found a rather cool tool you guys may or may not know about: http://pixologic.com/sculptris/
Sculptris is a great tool for freehand modeling. After that you can export and import into blender to finetune.
What i found it useful for was the modeling of everything with a nature look.
(so not so good for concrete walls/ramps/road)
Basically sculptris is a hump of clay you can shape. (even your 8 yr old nephew can use it)
There's also the option to create a flat surface instead of a hump, so you can draw your own terrain with it.
