Here is a list of my g-man sightings. feel free to add any I've missed:

1 - on a moniter screen in kleiners lab in chapter 2

2 - on the tv the vortigon is watching in the red carrige guarding the entrance to the old rail route in chapter 3 (be quick to catch this one)

3 - standing outside the old red barn as you arrive, chapter 4

4 - flickering on and off on a giant moniter attached to a building part way allong route canal, chapter 4

5 - standing on a walkway over the canal as you pass underneath, chapter 4

6 - walking away from the station along the railway outside the dock at the end of chapter 6

7 - look through the binoculars to little odessa on the highway, chapter 7

8 - on a moniter in nova prospect, chapter 9

9 - on a tv in a room full of junk just after you loose dog in city 17, chapeter 11 (be quick to spot this one)

10 - flickering on the giant moniter that the citizens pull down, chapter 11 (very hard to spot)

e-mail me for more precise descriptions if you need it.