Amazon Japan is an absolute no-go for me. Shipping is twice the value of goods most of the time, with no option at all to select something cheaper.
I want to buy albums (!), not renting the whole plane on which they transport their shipments....
Last time I did some calculations and it was actually cheaper to purchase something from Amazon.co.jp through a middleman (and then using SAL for shipping) than ordering directly from them.
Shops from which I usually order:
1) YesAsia
2) CDJapan
3) VGMWorld
4) HMV
5) Otaku
6) champs_des_pins@eBay
Like Amazon.co.jp I also avoid Play-Asia, since their inventory usually matches with the one from CDJapan, but the pricing is always higher. Plus their item stock management is a major catastrophe: I stopped counting the times where they canceled an order because the item was suddenly unavaible, even though their shop system clearly listed it as available. Their delaying tactics when this happens is another reason I eventually stopped using the shop.
Normally I just use 1) and 2) and 3). With all three I had very good experiences in the past. 5) and 6) are very expensive, especially their shipping charges, but they carry some rarer albums.