You’ll want to check out the Apricorn Aegis NetDock if you mostly use a netbook. This USB-powered device will offer you an extra four USB 2.0 ports. Two of them are powered and you also get a dual-layer DVD burner and a 2.5 SATA hard drive enclosure for future expansion.
It’s very portable too, measuring just 6.25″ x 5.75″ x 2.125″. It will cost you $89 and there’s a model that comes with a 5400 RPM 500GB hard drive already installed for another $100. Not bad at all.