If you want to build up a collection of parts, and have the space to store things until you need them, you may want to try some grab bags. Jameco has them, and I have heard other places have them too.
Don't online stores have HUGE shipping fees? The $3.50 or so ATmega328 will become MUCH more expensive. Very occasionally, I go to Sayal to get some parts. But, they only have some ICs (most of them I have no use for), some resistors, capacitors, switches, diodes, etc. The rest are things for computers that I have not interest in. They do not have everything I want. They don't have ATmega328 in store, either!