They are action figures. In fact they are action figures of one of the most popular games on the Xbox system. McFarlane is also know for having some of the best figurines ever made. I know I have a slew of them in my pad just cause they are so frigging cool to look at. That being said, you can now pick up the set of figures and play out you Halo fantasies like Darth Helmet in Spaceballs.
Here is a list of what is out now, there will be another set come June this year so if you don't see one you like here, just wait until then.