The BrikCrate has changed how my kids approach Lego. It was completely "build the set, forget about it" prior to installing it. Now they build like crazy in free form. http://www.brikcrate.com/
We just have three enormous rubbermaid bins with lids. Half the fun is searching for the right piece, and possibly finding an old lollypop stuck to it. The sound of kid hands pawing through a vat of legos is awesome.
Our daughter enjoys building too.