Recently I have been on the search for some quality 4x12 cabinets to go with the amp I'm building, that didn't cost life and limb. A lot of modern cabinets use particle board or fiber board, and the quality is just lacking as well as the tone. In my searches I found a company called StoneAge Custom Cabiniets . I placed a request for pricing, and within MINUTES I received a phone call from John Wheeler, the owner. He went over speakers, tolex, grille cloth, impedance, piping, EVERYTHING. These cabinets are AWESOME, and are as well built as anything that has ever been put out. 100% Baltic Birch plywood, and not the cheap shit you get at Home Depot. They come highly recommend from several people, and so I thought I would pass the info along here.
So..if you're looking for a speaker cab, check them out. Tell him I sent you.