There's also this guy from 5th edition with the special Cold One: Couple new blisters on Ebay at the moment.
Not bad for 5th edition. I wish they had kept the concept of "Horned Ones" in the rules as an special mount for Saurus Characters.
I am pretty sure that originally cold ones were mounted by skinks and later when the saurus cold ones were released, they changed the skink's beast's name to "horned one". A friend of mine who has been playing since forever told me that. Edit: Looks like he was right. Page 65 of that 5th addition rule book under Cold Ones says they are only ridden by red crested skinks. More on topic: The fact that our core is so limited is no mistake or in poor design. It's because Saurus, model for model can on average beat any other rank and file core unit. Someone has done calculations for it somewhere. I wish I had a link. But by design, not only are our core options limited, but our rank and file units are limited. Unless of course we are talking AoS where you can bring anything from anywhere anytime you want! In that case, I see no reason not to add light cav to the lizardmen lineup. You could just as easy bring light cav from any other army. Why not keep them thematic at least?