This site has a lot of good stuff (especially the T-Slot stuff) that could be VERY useful for building robots, especially larger ones, as well as light CNC machines or 3D printers. From what I saw on the web, they are good to deal with, have good quality stuff, and it isn't very expensive. They even have the price list linked right there on the website! I found it from here:
http://lumberjocks.com/Hutch/blog/2740 where this guy used it to build a table saw fence.