Software
ArcGIS
AutoDesk
Rhino
Plug-ins
Rhino:
Firefly
Kangaroo
Grasshopper
RhinoTerrain
T-Splines
Lands Design (have never tried this, appears to be usable but in development)
3ds Max:
populate:Terrain (generate terrain surfaces from contours)
Forest4 Pack (populate models with plants)
ArcGIS:
AquaVeo (water modeling)
Tutorials
General tutorial sites:
Black Spectacles (paid)
Design Reform (3ds Max, Grasshopper, Rhino, Illustrator, and more)
Digital Toolbox (Rhino, Grasshopper)
Lynda (paid)
Program specific:
3ds Max
ArcGIS
AutoCAD
Illustrator
InDesign
Photoshop
Rhino 5