Yeah shoptemp had to close and isn't taking any orders, it's being remade soon.
http://www.lightake.com/
http://www.0shippingzone.com/
Those are two sites gbatemp recommends, lightake in particular has a forum account here where they sometimes clear up confusions on products.
As for picking out the best cart, here's my copy-paste.
Note that the prices given are from chinese shops.
If you order from a shop in another country it's more expensive.
[*]
The original R4.
NOT "R4-III Upgrade", NOT "R4-SDHC", NOT "R4i NDSLL", NOT "R4 Red", NOT "R4 King"...
NOT ANYTHING ELSE WITH "R4" IN THE NAME! JUST "R4 Revolution For DS".
The cheap card for somebody that just wants to play games on a DS/Lite.
[*]
R4i Gold
The cheap card for somebody that wants to play games on a DSi with more storage.
[*]
Acekard 2i
Mid-range card for people that want to play games on a DSi/XL with some extra features.
[*]
EZ-Flash Vi
Higher-end card with even more features.
[*]
Supercard DSTwo
Pretty much the ultimate card right now.
- DS / DS Lite
The card will work on an original (fat) DS or a DS Lite.
- DSi / DSi XL
The card will work on a DSi or DSi XL as well.
- Game Updates
Firmware updates are what let cards play newer games, these are the life-blood of the card.
- SDHC
SDHC refers to SD cards larger than 2GB (gigabytes). If there's no SDHC support, you can only use SD cards up to 2GB.
- WiFi Update
The Acekard 2i can update it's cheats (and get minor bug fixes) over WiFi without having to connect to a computer.
- Auto Ap Bypass
Some carts have special features to ignore AP in most games, letting you play them without having to wait for a firmware update first. The Acekard only has partial support for this right now.
- RTS
The Real-Time Save (Save State) function lets you save and reload your game progress at any moment you wish.
- In-Game Guide
You can pull up text files and images in-game, in order to check a walkthrough or map you downloaded at any time during a game.
- Slow Motion
The card lets you slow down the game speed as you wish.
- In-Game Cheats
The card lets you create and modify cheats while the game is running.
- Special Homebrew
The card has multiple pieces of special homebrew, such as it's own GBA and SNES emulators, as well as text/PDF reader and video player.
- Battery Life
Unfortunately the DSTwo's extra CPU and RAM (which give it the special features) eat into the battery life a bit.