I just found the site I was looking for: http://www.edenspace.com which
sells plants that take arsenic from the soil. They are also experimenting
with plants to remove such contaminants as lead and uranium. I think it's
pretty cool what they are doing.

Initially I found reference to it at
http://www.raintreenursery.com/catal...ing%20P lants
The downside to this is the minimum order is 30 plants at $4.95 each
bringing the minimum order price to a whopping $148.50 plus
shipping/handling!

(Sorry about cross posting this to rec.gardens, because this is where it
really belongs.)