Euro profile cylinders are frequently used in UPVC doors. They come in single cylinder (one sided), double cylinder (locking cylinder on each side), and single with thumbturn (locking cylinder on one side and thumbturn on the other). They also come in various levels of security. The picture shows one of the top of the range (High security British Standard) that conforms to your household contents insurance.
You can also get a very similar cylinder to the Euro cylinder called the Oval cylinder, this cylinder is more of an egg shape compaired to the Euro cylinder.

RIM Cylinder, usually called a Yale lock. These are mainly used in conjunction with a nightlatch that sits on the inside of the door. These locks are usually low security but you can get a British Standard High Security nightlatch nowadays.

Mortice Dead Locks and Mortice Sash Locks a better lock. These also come in British Standard Insurance approved. The difference between the Dead Lock and Sash Lock is the Sash Lock has a latch on it that needs handles, the Dead Lock just needs keys.