There's some great online bong shops, here's a list of some of the most trustworthy sites around.

Grass City - Tonnes of bongs, pipes and smoking accessories. A top notch site.

EveryoneDoesIt - More quality bongs - including RooR bongs.

Weed Pipes - A selection of great weed pipes.

There's plenty more out there but these are highly regarded online headshops.