Single-sided PCB
Single-sided printed circuits represent the least sophisticated (and thereby least costly) of the printed circuit products.  These boards usually do not require plated through holes and only have a circuit pattern on 1 side.  Quite often single-sided boards are referred to 'punch and crunch' due to the fact that high volume runners are profiled with tool and die.

Double-sided PCB
Double-sided printed circuits are a step above single-sided in their complexity.  Double sided PCBs require plated through holes to provide better anchoring for soldered components and front to back electrical continuity.  Most designs require soldermask front and back along with a silkscreen layer for component designators.  Very often double sided designs utilize a mixed technologies of through hole (PTH) and surface mount (SMT).

Multilayer PCB
Multilayer printed circuits consist of 3 or more circuit layers bonded together by a thickness of insulating material called prepreg.  Prepreg is B stage epoxy impregnated fiberglass.  Multilayers are generally considered to be the most sophisticated printed circuit product due to their construction methods and design complexities. 

RF/ Microwave
Most RF PCB designs are considered to be functional components of the assembled sub-system.  These designs utilize various patterns in the circuitry to achieve changes in the characteristics of the RF energy field.  Tight line width tolerances and front to back registration are considered to be the rule when fabricating these PCBs.  Exotic materials such as: PTFE, Duroid, and ceramics are often utilized for their stability and dielectric properties.