To shed more light on esapersona and counterfit's writeups on the trombone:

1)There also exists a tiny piccolo trombone- although it's not commonly used.

2)The valve trombone works the in same way as do the trumpet, euphonium, and other valve instruments. The magical 'Superbone' does in fact exist- it's a trombone that has both functional valves as well as a fully-extendable slide, enabling the player to have the best of both worlds.

3)The trombone that esapersona refers to is the standard professional-model trombone: a tenor trombone with an F-attachment or F-connection. It is not a true bass trombone, but the extra pipes serve two purposes. First, they allow alternate positions (kinky). For example, on a regular trombone sans F-attachment/trigger, I would have to thrust my arm to 6th position (a good 2 feet out and bordering on discomfort) to play a 'C,' but with my trombone, I can play a 'C' in first position (the slide's home base, all the way in). Five other alternate positions exist, played with the trigger depressed. (There are only six positions that are in tune with the trigger depressed- there's no 'trigger seventh' because the slide would be on the floor at that point.) They are notated with the Roman numeral 'V'; for example, 'trigger 1st' would be notated as 'V1.' This is not just for laziness's sake; it becomes quite important in fast passages. The other thing that the F-attachment allows is an extended lower range.

4)Many orchestral music for trombone is written in tenor clef (middle 'C' is on the 4th line up, whereas in bass clef it's one ledger line above the staff).

5)The bass trombone is not really just 'a big tenor-' the difference lies in the bore, which makes it harder to fill up the bell.

An addition of my own, here's a short list of works that feature the trombone at some point (be prepared to play the excerpts at an audition):

Hungarian March and Symphonie Fantastique (Berlioz)

Ride of the Valkyries (Wagner)

Symphony No. 3 (Mahler)

Overture to 'William Tell' (Rossini)