Guanacos! We saw these guys nearly every day we were not in the mountains. They look a lot like llamas and are a favorite food source for the top predator in these parts, the puma.
On our last hiking day we got lucky and saw two pumas. We were in the van on the way back to the Eco Camp and saw some cars parked and guys with spotting scopes. They were about 100 m away, guarding a guanaco kill. It was definitely one of the highlights of the trip (thanks Roberto!)
We saw lots of birds, probably the coolest were the condors (which we saw several times) and the red-headed woodpecker.
And we saw a fox (actually saw a couple of foxes) near the trailhead on our last hike in El Chalten.