Yes, you can daisy chain USB hubs (i believe the original USB specs spcecified up to 128 devices!) but you may find if you use a high power drain device towards the end of the chain, you may struggle a bit. you can of course always buy a powered hub. I picked one up for about £15 from Argos, so you can probably get them a lot cheaper.
Or, you can add more ports via a PCI card.