Robinia pseudoacacia seems most likely.

Not a Robinia. Robinias have bipinnate leaves, and leafless racemes of pink or white flowers. Maybe Partridge Pea (Chamaecrista fasciculata)?

Some sort of Mimosa ?

Chamaecrista fasciculata is its name, commonly known as Partridge Pea. Native to the States, see below

http://www.ct-botanical-society.org/galleries/chamaecristafasc.html

Agree, but Tugbrethil, Robinia pseudoacacia does have yellow flowers.

Nope, Owdboggy. Check it out for yourself: always white or a very pale cream, except for some of its hybrids, which are various shades of pink to burgundy. It used to be a popular shade tree here in Phoenix, before we started trying to conserve water.