I have used Realhotstuff and Kickgaming/Kicktrading myself. Realhotstuff is in the USA (New Jersey) and currently has free shipping on the DSTwo (but not if you get a MicroSD bundle and they only have a 2GB and 4GB bundle). Kickgaming/trading is Canada based and shipping is almost as expensive as Shoptemp. For computer related stuff (such as a MicroSD card) I use Newegg and for recordable media (CD-R/DVD-R/etc) I have had good luck with rima.com. Assuming you live in the US I would recommend an 8GB or 16GB Sandisk MicroSD from Newegg and a DSTwo from realhotstuff. Note that there are two DSTwos that are the same price ($39) you want the one that says free shipping.
I was about to say, is saving $8 ($3 now) really worth the risk? All the other sites mentioned are good and bad. Sometimes they are great, sometimes they aren't. It depends on who you ask. ShopTemp is starting up fresh and it seems like they want to impress. Their prices have been lower than elsewhere on my purchases so far (SCDSTwo preorder). Shipping was faster than usual as well (granted I'm sure most of those DSTwo's were going to the USA so they went bulk). Customer service has so far been great. I for one wouldn't even mind paying a a few extra dollars more if it kept my mind at peace.
Edit: Just don't forget to click on the ShopTemp icon in my signature when you make your purchase