Haven't read through the entire thread, but Rightstuf.com has 40% off sales for various publishers, including Viz, Tokyopop, Del Rey and Dark Horse. I usually buy from amazon, but they generally don't discount viz or Tokyopop at all (unless you get lucky and they're included in a buy 4 get 1 sale), and these rightstuf sales are usually good on preorders, so I usually order a ton of stuff, which ships out a bit at a time, and by the time my last preorder is ready to ship, the next sale is active.
They are a fantastic retailer, especially when it comes to customer service. Their prices, especially on dvds, seems pretty high at first, but it's the sales that really drive the bargains... and if you're buying a bunch, it's worth the 12 bucks for their GotAnime membership to get an extra 10 % off.