Centurions are the term for the robotic Cylons (first seen onscreen in 1978). They were the first type to be created by the colonies. Though they are still around, the humanoid Cylons have become the higher order of the race, relegating Centurions to 'grunt' status, it seems.
The U-87 prototype served as the spiritual predecessor, and made its way into combat robots and even civilian models.
During the Cylon war, Cylon Centurions were present, along with gold coloured commanders. There also appeared to be two different types of centurion, a pilot model and a bulkier warrior type. There existed some Cylons of that era that were seen guarding a prototype basestar containing the first basestar hybrid.
A different model was seen in "Blood and Chrome".
The latest Cylon centurions have built in guns, and do not have a voice, possibly an indication that they have a lower status compared to the leading humanoid Cylons in Cylon society.