How much do those flash-carts for the DS cost btw? Wouldn't mind getting into the homebrew scene for it, as there appears to be some goodies people made for it.
It varies depending on what you want to do, but most DS homebrew works fine with a GBA Movie Player (with hacked firmware).If you have a CF card, I would recommend it as it is the least expensive homebrew cart I have ever come across.
Since DS homebrew started off with all sorts of compact flash adapters, lots of stuff actually makes use of FAT file system stuff to read and write files or game content. (I believe Quake DS is using resources stored on the cart instead of the NDS file, since only GBA carts allow us to run binaries over 4 MB at the moment).
This is all because it began using Slot-1 for a passthrough device, which tricks the DS to run unsigned code off the GBA slot, so the best way to go was clearly to stick with GBA slot to hold the code. (And people really liked the GBA Movie Player at the time).
Even though the DS card encryption is now finally cracked, there is so much homebrew that makes use of those Compact Flash carts that noone really wants to bother switching over to boring old DS cards. (I don't anyway :P).
Other CF adapters are Supercard CF and M3... Supercard is less expensive and smaller than the M3 but seems to get very mixed reviews, while the M3 is all-round pretty decent, but just as huge as the GBAMP. (GBAMP is the size of a GameBoy Original cartridge).
If you don't have a CF card, there are some SD versions of these things, too. And, come to think of it, if you're interested in the removable storage medium methods of DS homebrew, I guess your best bet is one of the SD ones anyway as they are generally about the size of a GBA cart, which is much more manageable than the CF card things. (GBAMP just about doubles the size of a DS Lite).
Of course, regular GBA carts like Eikon has will fit best and generally do what you want.
Careful if you do decide to flash your DSL's firmware, by the way... there have been reports of it being easy to brick because a careless hand can accidentally bridge a circuit which conveniently causes a fuse to blow.
Thankfully, you don't really need a PassMe2: There are a few "nopass" devices (One which I know by name is Datel's Max Media Launcher) which are the size of a DS Card and work easily since they make use of the finally cracked DS Card Encryption to do the passthrough stuff. (Yay!).
If you do decide to flash the DSL's firmware, I'll point you here. (Actually, I'll do it right now).
Video also shows the snug fit of the MiniSD Supercard. (Note that homebrew currently doesn't play nice with accessing the SD card there, but I imagine that will be fixed soon enough).