The Orchestra
The Orchestra: A User's Manual Tubas
A terrific resource covering many aspects of the tuba. Most explanations are made with video and audio clips of members of the Philharmonia Orchestra. Be sure to check out the players tips and tricks section.
Other
Tuba Euphonium: Some More Thoughts About the Tuba
This site is a guide to learning how to play the tuba.
Oxford University Press
Ou Pblog: Ten Facts About the Sousaphone
This blog provides information about the development of the sousaphone, the similarities and differences between the sousaphone and tuba, and the kinds of music groups that use sousaphones.
Dallas Symphony Orchestra
Dallas Symphony Orchestra Kids: Tuba
Read about the brass family, and the tuba in particular. Use RealAudio or Windows Media Player to listen to the tuba by itself and with the orchestra.