http://www.supercardstore.com
Flashing the DS means you can't brick it- which is good. It also means you can have a proper DS game in the top slot, instead of a passme thing, and you will still be able to run homebrew.
From that website (supercardstore), you will need either a supercard SD, a supercard CF or a supercard light. supercard SD is your best bet unless you have a DS lite, or already own a CF card.
I dislike the CF version because it leaves some of the CF card sticking out. On the SD version, it is completely encased in the supercard, so no accidents can happen. SD cards also go in the wii, which is good
I'll mail you my passme if you want, else you'll need one of them as well. Once you get it, just flash your DS and then mail it back. Then you need an SD card writer (though you can host stuff on the internet then download it with a program, so you'll only need it once). I use
this one and it is fine with my 2 GB SD card.
For the SD card, get a decent make if you're storing important stuff on it, or I know someone that may still be doing cheap unbranded 256 meg cards, if you're interested. Don't expect any help when they wipe on you, though.
my setup:
DS phat, flashme ver.7, supercard SD, 2 GB kingston 50X SD card.
If you want to watch video's, you may be better of with an 80X- i get a bit of lag occassionally. I'd recommend getting something that does fat32 formatting, because then you'll be able to put insane amounts of data on it.
edit: technology seems to have moved on considerably in 6 months, I recommend doing a bit of research on the top slot micro SD things. X9 looks good, and so does the supercard DS.