I think there was a ''venerable'' also
Found some variant names here:
http://whfb.lexicanum.com/wiki/Steam_Tank
Not sure how accurate they are, but I do recognise the pictures; they're from the old White Dwarf article that described the fluff behind these variants. I think the 'Von Zeppel' is correct, and I don't know about the 'Alter Kamerad' name, but that's definitely a Volley Gun in it's hull....
I have the Empire collectors guide
"Conquerer" is the basic steam tank with a steam cannon and turret gun. Pretty much all the current set makes. They missed a trick with that kit, they could easily have made variants in a plastic kit.
"Sigmar's Hammer" has no cannon, or turret, but is closed top, and has a bedroll on top. Has more flags/pennants an alternative chimney top
"Von Zeppel" had the fighting platform, but no cannon or gun, an alternative chimney
"Old Reliable" has a 3 barrel volley gun, a standard pole and other baggage bits
"Implacable" has the open top. It has a mortar, it did come with a thing for the mortar, and a metal mortar, but pictures show it converted with the current plastic mortar. It didn't have mortar crew though, so those are usually added from the cannon set. It did have an alternative chimney and other bits. *Edit* it also has steam Swivel guns on attached the hull
Those were the only ones that were made available as kits to buy.
There was one called "Deliverance" or something, that had a trailer which was a spare bolier and wheels, mounted on the old metal helblaster, or could have been the old metal mortar carriage. I can't see how the extra boiler would work since there's no way of filling it, so must be dragged around as spare parts. That one was somebody's own conversion though, so not an official one, though it was featured in White Dwarf, and I think added to the named list. N.B. "Deliverance" is named as a steam tank in the Battle for Nuln in The End Times: Thanquol. And in The End Times: Glottkin, the steam tank saved from Talabheim is "Miragliano"
I have also seen Von Zeppels with the volley gun part, but that's not the official build for it.
Then there was the Halfing Soup Tank "Kathleen"