Here's an implementation I wrote some years ago that includes obstacle avoidance. Clicking adds obstacles, spacebar adds boids, reloading gets new colors. This ended up looking somewhat like sperm avoiding eggs...

http://humortree.org/projects/flock03/

(Java applet warning!)

The source code is here:

https://github.com/mccutchen/humortree.org/tree/master/proje...