You can compare prices and locations for these at ShopTemp.http://www.r4is.com/gateway-3ds-flash-cart-for-playing-3ds-roms-on-3ds-and-3ds-xl-p-4.html reliable US based reseller out there and it's what I use
Throwing in my vote in for a Supercard dstwo too, when I was looking to get a card , http://www.r4is.com/supercard-dstwo-best-3ds-flash-cart-for-3dsdsids-lite-p-3.html it seemed team to be the best, I have owned it for half an year now and I love it
The first wood gold r4i card is the best out there,http://www.r4flashcart.com/8-wood-r4i-gold-3ds-flashcart-for-3ds-xl-3ds-dsi-and-ds-lite.html that's what I use, it has real time saves and allows you to play ds games on 3ds and ds lite
new smilie ^
its much better than the rest (except for the fact that only touhou fans really understand it and im not a touhou fan and yes its bad apple thats like the testing thingy
)