I have a 30GB 5G iPod, and today I ordered one of the refurbished shuffles. I figured this one would be convenient in certain situations, especially if I can ever get my lazy butt doing anything active.
Seriously a good idea though, the shuffle you can set to manually manage it in iTunes, or you can have iTunes autofill it.
I use the "Only add check marked songs" to fill the smaller ipods I have and the bigger ones I have carry my whole library.