Types of trucks
In general, we can say that there are 3 types of trucks: RKP’s, TKP’s and Conventional trucks.
RKP (reversed kingpin): Trucks that you can find on most of the longboards. They turn more and are more stable. On most of your basic completes you can find Cast trucks in around 180mm.
There are different materials and techniques used for making trucks. You have CNC machined (precision) trucks, Forged trucks, and Cast trucks. Trucks also come in different widths.
TKP (traditional kingpin): Mostly used on street setups, these trucks are less turneble, but at the same time quicker in their response. They are also lighter, so it is easier to do tricks with them. Next thing is that these trucks are usually made with grinding in mind. You can find TKP trucks, most likely on skateboards or cruisers.
Concept trucks/Surf-skate:  These trucks are usually designed with even deeper turns in mind, or faster return to the center, to allow you  to pump easier. These trucks are usually really fun at lower speeds, but will not be safe for higher speeds.