Everyone keeps telling me to buy a DS flashcard

[GrooveMan.exe]

They all have different properties. All of them will run old ganmes fine, but newer games have better emulation protection; so they run variably. In the long run, all flascarts will eventually run any game; either via updates of the firmware themselves; or patching of the roms.

R4 and M3 Simply are essentially the same firmware; although R4 is no longer officially updated. There's a fan homebrew version of this called YSMenu. None of them work on the DSi. I had an R4; but gave up on it when it couldn't run M&L3 or KH358/2.

CycloDS is the flasy one with lots of functions. It boasts the ability to do save states, and to access options even while playing games. It's newest incarnation might run on the DSi, but don't quote me on that.

AceKard is the emulation extrodinare one. It runs most games with minimal to no patching (althogh some piracy lockouts do need to be navigated still). The newest model - the AceKard 2i is the one I use. It can run on the DSi; natch. However; because this firmware is so self reliant. If a game comes out that it can't run; it's usually the last to get a patch for it.