As many people know the DS is backward compatible with GBA games, however many flash carts were designed around the design of the GBA and SP so fitting the carts into the DS can sometimes cause problems.
Some other Romcarts simply refuse to boot on the DS.
I can happily now confirm that the following GBA Rom Cartridges work flawlessly with the DS meaning Homebrew GBA work can easily be continued!
All tests were done on my USA DS.
EZ2 PowerStar (Personal Favourite) - Fits perfectly and super setup in my opinion. The EZ2 PowerStar has a new architecture to save battery drain!
EZ-Flash 2 EZ-Cart - As the EZ2 Powerstar without Power Save Feature
GBA QBus / QBoy - Good fit, slightly tight but works fine!
XG-Flash - Good fit, works fine!