I use a 1 GBit serial flash. Very simple to attach through the SPI bus. You need to make a driver though and that can be a little bit tricky. If you can not find such a memory (mine is a BGA, you maybe do not want that), there are lots of parallell flash that you can use. If you are a hobby designer, check for some USB memory stick and steel the circuit from there. You will learn o lot of soldering too this way ;-)