Theres also a 20gb HDD but dunno if its still available in stores. U can check with all the reputable game stores and see if they have or alternatively do a search in the pasar malam section, im sure theres plenty of 2nd hand drives for sale there.

I'd say with the NXE out and install capabilities, why not invest on a HDD and save ur dvd drive from overworking. Just my 2 cents.