My biggest is a 2TB samsung ecogreen which I was using for media streaming, but then I had to have the big PC switched on. So I bought a 1TB NAS, which is probably the neatest.

Smallest - the Revo only has a 160GB HDD but it's only going to have the OS and a few programs installed, with probably very little actual data.

Other than that... a 20GB ipod or my wife's 5GB Zen mini.