Some spiders can produce different types of silk, each for a specific purpose. How many types of spider silk are there?

There are seven different types of spider silk produced by seven different silk glands.

According to http://www.chm.bris.ac.uk/motm/spider/page2.htm the seven types of glands are:

Achniform gland: swathing silk.
Cylindriform gland: egg sac silk.
Ampullate glands (major and minor): non-sticky dragline silk. Silk from the minor ampullate gland is only half as strong as that from the major gland.
Pyriform gland: attaching threads - attachment discs are made which anchor a thread to a surface or another thread.
Flagelliform gland: core fibres of sticky silk.
Aggregate gland: outer part of sticky silk - droplets of an adhesive substance are deposited along the threads.

Some more info:

Many species of spider have different glands to produce silk for different jobs, such as housing and web construction, defense, capturing and detaining prey, or mobility. Thus, different specialized silks have evolved with material properties optimized for their intended use. For example, Argiope argentata has five different types of silk, each for a different purpose:

dragline silk: Used for the web's outer rim and spokes, as well as for the lifeline. As strong as steel, but much tougher.
capture-spiral silk: Used for the capturing lines of the web. Sticky, extremely stretchy and tough.
tubiliform silk: Used for protective egg sacs. Stiffest silk.
aciniform silk: Used to wrap and secure freshly captured prey. Two to three times as tough as the other silks, including dragline.
minor-ampullate silk: Used for temporary scaffolding during web construction

https://en.wikipedia.org/wiki/Spider_silk#Types_of_silk