This #96995 UNSC Warthog is from Mega Bloks. It's part of the Metal Series. It's made to look like it's Lego but at this size I don't think any will fit. The base is two pieces and is held together by a 4×2 flat piece, with connections on all four sides.
It's priced at $10 which is a little steep. I've managed not to buy any of the action figures, vehicles or Mega Bloks sets or Mega Bloks 12″ Halo figures so far so I decided I could afford this one luxury.
Boy, just writing about it makes me want some.
There is a UNSC Scorpion #97039, Covenant Banshee #96994 as well as a few figure packs. The Warthog, and probably the Banshee, appear to be around 1:64 scale so it fit into my collection well.