I'd like to recommend a source of metals and plastics to add to the the Links page: Online Metals Online Metal Store | Small Quantity Metal Orders | Metal Cutting, Sales & Shipping | Buy Steel, Aluminum, Copper, Brass, Stainless | Metal Product Guides at OnlineMetals.com
. They have a huge and growing selection of aluminum, stainless, brass and all kinds of plastics in both sheets and lots of different shapes. They sell the plain old materials as well as some of the more exotic stuff. Their prices are surprisingly good and they ship relatively fast. They will cut your material to size, one piece or 50. If you live far from a big city where you can usually find this kind of stuff, this might be where you'll want to shop. I live close to Chicago and I still buy from them because their prices are so good. They have warehouses in both Seattle and Cleveland. They even have a program for discounted shipping to Canada.
They also put insufferably bad jokes in their web site.
I used their 5052 aluminum alloy to cover the bottoms of my new floor panels.