Courtesy of SpaceRak

This is the most common design of pallet racking used.  The standardized "teardrop" connection design makes the uprights and crossbeam interchangeable with those from other manufacturers.  This design is very versatile and the boltless design simplifies reconfiguration of beam levels.  The alternative to boltless racking is structural pallet rack which is assembled with mechanical fasteners (usually bolts) and may offer higher capacities.  Structural pallet racking is also sometimes designed into the structure of the building itself supporting the roof and eliminating the need for I-beams.

Courtesy of Steel King Industries.

This shows the most common configuration of selective pallet racking where single pallet depth racking is placed back to back. This configuration can be used with wide aisles (more than 11') using a standard forklift, in narrow aisles(8'-10') using a reach truck, and very narrow aisles (less than 6') using order selectors, turret trucks, and swing mast trucks.

Courtesy of Steel King Industries.

Racking system that incorporates a carriage or other sliding device to allow you to feed multiple pallets into the same location "pushing back"  the previous pallet. Can be used in wide aisle and narrow aisle applications.

Courtesy of Steel King Industries.

Racking system which uses some type of gravity conveyer system built into each racking level.  Pallets are loaded in one side and flow to the other side for picking.  Works well for high density storage where first-in-first-out (FIFO) rotation is necessary.

Courtesy of SpaceRak

Racking system designed to allow a lift truck to drive into the bay creating very high density storage for non stackable loads.  Useful for operations with limited SKUs and high quantities of pallets per SKU.  FIFO is difficult to maintain in Drive-in racking systems

Courtesy of Paltier

Racking system in which the shelving supports are connected to vertical supports at the rear of the rack.  There are no vertical supports on the face of the rack allowing for storage of very long pieces of material such as piping and lumber.

Courtesy of Nashville Wire Products

Wire decking can be used with Selective Racking and Cantilever Racking. Generally used when product is placed into racking without pallets.  Due primarily to safety reasons I am a big proponent of wire decking even when pallets are used. Wire decking increases worker safety, productivity, and reduces product damage.  There are other types of decking available including solid decking.  Fire inspectors generally do not like solid decking since it reduces the effectiveness of sprinkler systems.