I know from the beta, how to access and use a few commands to spawn Citizens, Antlions, Zombies, Headcrabs, Combine Soldiers (I'll try to get all of them.. (metrocop etc) and possibly a few other things like sentry turrets or manhacks..(might take a bit to find those out though)
I can also detail how to give them guns, allow them to act like squadmembers do later in the game, and set up binds or commands to make random battles hehe... I had a few 3 way wars with Combines, Citizens, and Antlions all on a beach.. very fun.
I spent hours figuring this out so maybe people can have fun too..\
EDIT: Only reason I'm 'polling' this is because it would take a bit to detail it...