Because they're so canon.
The Clues In Front Of Us by solaras. It's a WIP, but steadily updated every few days, and it's absolutely what I was looking for in this pairing. (more Gordon/Bruce than Gordon/Batman, mind you :D)
All Kinds of All Right by sua_lay. Gordon, Batman, and Jimmy Gordon. It's adorable, and sad, and lovely. Could be pre-slash, doesn't have to be, but it's wonderful.
Reveal Batman/Gordon, unmasking.
First Priorities by jen_in_japan. Commissioner Gordon gets locked up with a most useless person ever, Bruce Wayne. It's brilliant. Gen, suppose.
Getting Close by jen_in_japan. Jim Gordon doesn't know how he ended up with a playboy billionaire for a lover, and he tries to keep it that way. Gordon/Bruce.
Dropping Masks by rhye. Bruce/Gordon.