[mjobling]

James,

Wikipedia also has good articles on them all:

Class 01
Class 02
Class 03
Class 04
Class 05
Class 06
Class 07
Class 08
Class 09
Class 10
Class 11
Class 12
Class 13
Class 14

Some of them bring back great memories, such as wandering around knackered old sheds in Scotland in the early 80s looking for forlorn Class 06s, and peering through the crack of the shed at the disused class 01s in Holyhead.

Wikipedia also has stuff on the history of diesel locos:
http://en.wikipedia.org/wiki/Diesel_locomotive#History