Cougar
From Halopedia, the Halo wiki
The Cougar is a lightweight, fast and highly flexible, versatile AFV constructed by the UNSC that was to be used in the upcoming game Halo Wars by UNSC forces. Although heavy armor fire would eventually blow the Cougar away quite easily, this vehicle was highly effective holding and fending off enemy armored vehicles while slower friendly armored units are in transit to the battlefield. The Cougar had gained infamy in several urban tactical situations prior to the deployments in the war against the Covenant. [1]
It appeared as a somewhat standard armored fighting vehicle with a pair of wheels up front and four in the rear. It bore a small mounted turret armed with two auto-cannons and a windscreen on its forward body with two side windows to provide a fairly high amount of visibility for the driver.
According to Ensemble, the Cougar has been cut from the game in favor of other vehicle ideas. Though it could have made a cool addition to Halo 3 [2]