I'm new to this and I am looking for the right product for the nintendo DS. I've searched and found: G6 Lite 4Gb with Passcard, DS-Xtreme 4Gb, M3 Simply, R4, SuperCard Lite Rumble - MicroSD [Black. Which one will play "NDS roms, GBAroms, snes roms, movies, music" without having something stick out of the NDS? Also, I am going to be using it on both the original NDS and the NDS lite.
As you want GBA support you do not want to buy the DS-extreme, M3DS Simply, or R4DS as they are all slot-1 (no GBA support) Which from your list leaves the Supercard or G6. As you want to use the device in both an original DS and DS Lite that then leaves the G6 (as you can purchase a full size GBA case for it) However you are limited to only 512MB of space (4Gb = 512MB) I would recommend either the M3 MiniSD or M3 Lite (both with a Passcard3) As these use external media you can choose how much storage you want, the M3 MiniSD is GBA cartridge size and uses MiniSD cards, it fits perfectly in the original DS but will stick out of the DS Lite slightly. The M3 Lite is the same size as the DS Lite slot-2 dust protector, it uses MicroSD for storage, ti fits perfectly in the DS lite, but does not fit in the original DS without purchasing a replacement GBA shell for it, replacing the shell allows it to fit in the original DS perfectly, switching between the cases reguarly isn't recommended as you have to unscrew the case and remove the circuit to place it in the other.