For those reading this thread I caution "caveat emptor" - "let the buyer beware". Not much in life is free, so if you register at the above mentioned site and give your personal information, know that you might be subject to spam in the future.
There are many 'free tree' programs in several cities in the US, and a google search can often turn these up. Arborday.org also will send you 10 free trees (whips really) when you join for $10.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.