But do you know whats really funny... I only heard about these things recently (yesterday) and you happened to hear about them at the same time...... did you stalk my msn......... *quickly looks both ways*
The site LukeMayn said is good for all the DS Flash Carts. I would advise you to not to get the R4 as it is expensive compared to some of the other ones out there, and after all, they mostly all do the same thing. www.dealextreme.com or you could try find a store around your area that sells them.
I have a SuperCard DSONE, and I have to say, it's about as good as I can imagine. From the little research I've done, the DSONE has the best compatibility with homebrew and *ahem* "backups". I have never had a problem trying to run anything, and it has never crashed/frozen on me while running.