I like the tormach ones but at only 10mm they are kinda thin.
32836 - Aluminum Fixture Plate, 18"x8"x10mm
I need to make a few fixtures and wanted something thicker to work with. So I found some 1" thick ones.
In order to get a decent price I had to get a few. If anyone is interested, I have extras I can sell at $85/ea. (They fit in a flat rate box, so $20 shipping for up to 3)
For your convenience: http://cgi.ebay.com/ws/eBayISAPI.dll...m=261248231619
I can also get 2" thick ones for around $150.