M.E.
We use a rolling microwave cart for Legos. The pieces go in a clear shallow bin in the cabinet underneath the cart. This way he can dig around to find the right pieces he needs. I've tried sorting the pieces, but he ends up dumping them all back into the large bin and digging through them anyway!
What I like about the cart is the safety for my 1-year old toddler from the Legos, and the Lego's safety from my toddler! Any works in progress are stored on the top of the cart. It has a 1" rim to keep pieces from sliding off, and we attached two large lego mats to the top to anchor the pieces to.