That's why we think CYBER Gadget's CYBER Familator Lite is so great. Based on their CYBER Familator "Famiclone," It plugs into the DS's GBA slot and allows the system to play genuine (and pirate, we suppose) Famicom cartridges. And, with the right Gyromite cartridge, it'll play American games too. It even has TV out, making it a fully functional Famicom!
It'll be out in Japan next month, but CYBER Gadget has yet to announce the price. The amazing name will probably bump it up an extra 1000 yen or so. Familator.