There are actually several members of the clarinet family, of which the Bb soprano (pictured above) is the most common. This instrument, colloquially known as the "licorice stick", occupies a position in the concert band that is similar to that of the violin section in an orchestra. A full concert band may have as many as twelve Bb soprano clarinets, divided among three parts.
Alto and bass clarinets are less common, but when available they add depth and colour to the low woodwinds. The Eb clarinet and relatively rare contrabass clarinet round out the high and low ends, respectively, of the range.
Like the oboe, clarinets are typically made from the wood of the Mpingo tree (also known as "grenadilla wood" or "African blackwood"), although student models are often made of plastic.
Here's a collection of pointers to various places in the Web that discuss the clarinet: