Portal 1, 2 & upcoming 3

[Mario-Fan]

-in portal 2, wen you go into the robot enrichment and go into room 6, GLaDOS will briefly talk about Chell, referring to Chell as "Her," or "she."

You mean it wasn't already blindingly obvious that Chell's a girl? You can actually see that (even in the first game) if you put two portals next to/above each other, the portals will act a bit like mirrors and show this weird girl in an orange suit with dark hair, a ponytail and a portal gun.