One way uses lloyd's algorithm. Daniel Piker posted an example a while back: http://www.grasshopper3d.com/group/hoopsnake/forum/topics/lloyds-al...

I use a Daniel Piker script

http://www.grasshopper3d.com/group/kangaroo/forum/attachment/downlo...

from this discussion

http://www.grasshopper3d.com/group/kangaroo/forum/topics/circle-pac...

and I add some random sort depending on the Colour Brighness, because the number of point depend on the surface of the circle sorting is done according to the square of the radius (R1/R2)^2. 

You have to enter the number of point needed to fill the space, multiplier could be used to adjust well the filling.

I'll post the definition later today after cleaning it up a little...