The Rebel Alliance has been depicted using quite a variety of ground vehicles in various extended universe sources, here are the ones I know of as depicted in Video Games.
In Star Wars: Galactic Battlegrounds the Rebellion can construct 2 "Tank" vehicles: The T1-B hovertank is a small, shielded Anti-Infantary repulsor tank wheras the T3-B heavy attack tank is a tracked heavy tank designed for taking down larger vehicles and noted for being able to take on ATAT walkers in open combat. The game also features a collection of generically designated artillery and anti-air weapons platforms. One of note appears to be the Mobile Proton Torpedo Launcher, an artillery platform that could fire while moving. These units also appear in Star Wars: Force Commander.
In Star Wars: Empire At War the Rebellion instead construct the T2-B repulsor tank which furfills a similar anti-infantry role to the T1-B. IIRC the T2-B supposedly was designed originally as a mining transport, it's repulsors being to help it move over rough terrain and shields to protect it from landslides. Similarly the T4-B heavy tank is an "upgrade" of the T3-B and similarly is the Rebels' anti-vehicle tank in said game. Finally the rebels can also field the MPTL-2a deployable artillery, which unlike its predecessor the MPTL from Galactic Battlegrounds has to be deployed to fire. (Interestingly the T2-B seems to be the only Rebel tank to have appeared in a new canon source)
Star Wars Battlefront 1 (2004) features the armoured hovercar Rebel Combat Speeder, which was apparently effective against both infantry and light vehicles. Also apparently appeared in Galactic Battlegrounds as a "Mech" unit.
Star Wars: Battlefront 2 (2005) has the rebels using instead the AAC-1 speeder tank, which fills a similar role to the rebel combat speeder, although its large rotating missile pods give it a more tank-like form and presumably an easier time combatting heavier vehicles, although it does not feature in the Hoth mission so there is no indication as to how it would deal with an AT-AT.
Sources: mostly wookiepedia and personal experience with the games mentioned.
For the most part tanks were not fielded very ofted by the Rebellion as most of them were either smuggled on the down low from corperations sympathetic to the rebellion or had to be constructed by the rebels themselves.
Note: The Rebels did have other Anti-Vehicle units such as the dish turrets seen on hoth in Empire Strikes Back and Plex rocket soldiers which could also have been used to take down an AT-AT. Also according to Star Wars: Empire at War it was uncommon but not unheard of for a AT-PT artillery walker to fall into the Rebellion's hands, AT-PTs being very effective anti-vehicle walkers.
Sources: Wookipedia, Gamefaqs, personal experience with several of the games mentioned.