The surrounding material in a composite is called the matrix. The reinforcing material that is surrounded is called the phase or the reinforcing phase.

Fiber Reinforced Plastics

[Polyurethane] is often reinforced with chopped glass fibers. The glass fibers increase the stiffness of the composite material and act as a cheap filler.
High strength [nylon] resins like Zytel by DuPont can be reinforced with chopped glass or glass fibers.
[Epoxy] is often reinforced with glass fibers or carbon fibers. Many aerospace composites are made from this combination.
Ribbons or mats of reinforcement fibers may be used as well.
The first [fiberglass] railroad car, a hopper car called the "Glasshopper", was the only car not destroyed in a catastrophic derailment.

Sometimes a coupling agent often must be used to make the reinforcement fibers stick to the plastic matrix. Silane is frequently used to make glass fibers stick to an epoxy matrix. When the reinforcement breaks free from the fibers due to stress, delamination occurs. This dramatically reduces the strength of the composite.

[metal matrix composite | Metal Matrix Composites]

Metals must be reinforced with other metals that have a higher melting temperature, or with ceramic materials. This is a still relatively new frontier in [metallurgy].

Tank armors are often made from metal matrix composites. Carbon-based ceramics can not be used to reinforce steel armor because they will dissolve. For this reason, boron nitride is often the preferred reinforcement material.
Carbide Drill bits are made from tungsten carbide particles embedded in a cobalt matrix.
Aluminum diboride flakes can be used to dramatically increase the stiffness of aluminum.

Manufacturing Techniques

The most common [manufacturing] techniques for composites are

hand layup
filament winding
resin transfer molding
reaction injection molding with filler

As a Hobby

Some people make their own composite [kayak | kayaks], [canoe | canoes], [model rocket | model rockets], and even aircraft in their garages. A great deal of care must be taken to get good ventilation due to the often toxic fumes that come from curing epoxy and other plastic resins.

Composites on the Web

http://composite.about.com

composite material (thing)