I like to learn by example, I just go to the project announcements board here and look for cabinets that are along the lines of what I want to do, then I pull what I like best from those projects.
As far as other forums, there isn't much else out there that I know of. This is the site for DIY acrade controls. Shoryuken forums might have some control panel design stuff specifically for people who are into fighter games, and primarily for using with console systems. They would pretty much be 1 player stuff as well.