I've just released TreeGen, an interactive 3d tree creation program!
I've been working with drawing plants, in one form or another, for the last couple of years. The first method I tried (back in 1999!) was a true L-system, where a list of drawing commands is generated and used to draw the tree. I've also explored using fractals, drawing the classic fern, among other shapes. The method I'm using now is recursively adjusting and drawing the tree, which might be considered a hard-coded L-system. In any case, I had a lot of fun writing and playing with this program and I hope you do too!
TreeGen v1.0 src + exe (about 165k)