Fibonacci in Grasshopper

http://www.grasshopper3d.com/forum/topics/fibonacci-square-sequence

Includes a link download a definition to form a Fibonacci spiral in GH

 http://www.grasshopper3d.com/photo/test-no1fibonacci-bridge?context=user

Another example of someone exploring how the Fibonacci sequence might manifest itself in a structure

 http://eat-a-bug.blogspot.com.au/2009/08/fibonacci-tiling.html

This page also includes a GH definition to create the pattern above. 

Voronoi

Parametric Wood

"The Parametric Wood seminar is an advanced digital design research seminar focused on contemporary timber fabrication and long-span structures enabled through parametric design in Grasshopper."

Lots of information and resources on using Grasshopper to generate designs to be fabricated in wood

2D Branching Structures using RABBIT

The definitions show how to create 2D Branching Structures using RABBIT.
More about Branching Structures: http://algorithmicbotany.org/papers/abop/abop-ch1.pdf
The meanings of the symbols:

F move forward at distance L(Step Length) and draw a line
f move forward at distance L(Step Length) without drawing a line
+ turn left A(Default Angle) degrees
- turn right A(Default Angle) degrees
\ roll left A(Default Angle) degrees
/ roll right A(Default Angle) degrees
^ pitch up A(Default Angle) degrees
& pitch down A(Default Angle) degrees
| turn around 180 degrees
J insert point at this position
“ multiply current length by dL(Length Scale)
! multiply current thickness by dT(Thickness Scale)
[ start a branch(push turtle state)
] end a branch(pop turtle state)
A/B/C/D.. placeholders, used to nest other symbols

http://morphocode.com/work/rabbit/tutorials/2d-branching-structures-with-rabbit/