Half-Life 2 Beta Screenshot #1
Half- Life 2 Beta Screenshot #2
Half-Life 2 Beta Screenshot #3
Father Grigory
Roller Mine (I think these were in one of the trailers...)
Another deadly but annoying small electrical enemy added to the fray, Roller Mines are glowing devices in Half-Life 2 that will when you're driving a vehicle attach themselves to it and siable the vehicle from operating at all. If they are on your foot, they will zap you with electricty. You can find these roller mines scattered across the roads outside City 17.
And here's a coouple of monster descriptions:
Fast Zombie (I showed you guys a screenshot of these guys a while ago)
Just when you thought the mawman zombies couldn't get any worse, now there is a new form of the zombies in Half-Life 2 that can leap and swing from trees, run at insane speeds, and swim underwater! These new zombies are found hanging out in the Ravenholm graveyards.
Poisoness Headcrab
Just when the headcrab seemed like it was almost a harmless alien, now in Half-Life 2 there is a poison infecting version of the headcrab that can as well transform you into one of its zombie friends so watch out for them!
Most of this stuff was taken from a couple of sites I go to on a daily basis.