For used equipment, I like www.keh.com and www.mpex.com. And of course if you want to bring in lots of business, just link to the choice categories, like LF Lenses, on eBay, since at least half of those old shutters need a CLA.
For film and chemicals, www.jandcphotography.com, www.bostick-sullivan.com, www.artcraftchemicals.com, and www.photoformulary.com
For info, there's www.apug.org, lfphoto.info, graflex.org, f32.net
This guy doesn't seem to have his website set up yet, but he made me some really nice custom filmholder belt packs for Grafmatics and for the 5x7" bag mags I use with the 5x7" Press Graflex--http://tedsphotogear.com/