So - I have been re-reading books in the City Watch arc. To date I have read:
Guards! Guards! - Sam Vimes, Carrot, Colon and Nobby are introduced here. Vimes is an alcoholic - his way of dealing with being both an idealist and a cynic, and this is the start of his 'redemption' arc. One of my favorites.
Men at Arms - The Patrician has introduced the concept of 'diversity' and forced the watch to take some new recruits: a dwarf, a troll and a woman. This book introduces us to Angua. Also one of my favorites.
... and now I am reading The Fifth Elephant