I'm selling this Flash Cart and USB Linker with XP/2000 software since I just sold off all my GBA stuff on eBay.
It works as new and allows you to upload/download roms and save games to/from the cartridge via a PC (I only recommend using this for Homebrew applications and not for any copyright infrigement!!) It is your choice what you do with it, but I do not recommend breaking the law.
Works with GBA and GBA SP.
Depending on the game you can get between 4-8 games on this cart at a time and it has a boot menu so you can choose which to run at startup. It saves you lugging all your games around with you (that you own!).
The cart will be blank when I send it, so no games on it. I'll burn a CD with the 2000/XP drivers and software on for you, it's also avaliable online.