What are the names of the vehicles to provide assistance to aircraft during the turnaround?
The most common vehicle seen is the tug. 


source

source

Tugs are multipurpose tractors that are used to tow around all sorts of things. 



Several types of equipment are shown in this diagram:


source



The tow vehicle at the nose is more commonly referred to as a pushback tug. They come in different sizes. Here is an example:


source



The GPU is most often a unit that is towed behind a tug.

source



Belt loaders usually can be driven on their own:


source



The wide loader is used to put cargo containers in the hold:

source



The cabin cleaning truck and galley service truck often have a lift built in:


source



Luggage can be brought in baggage carts 


source

or in cargo containers which are brought to the aircraft on dollies

source



Another vehicle often seen is the people mover:


source