"Amongst extant reptiles only two lineages are known to have evolved venom delivery systems, the advanced snakes and helodermatid lizards (Gila Monster and Beaded Lizard)1. Evolution of the venom system is thought to underlie the impressive radiation of the advanced snakes (2,500 out of 3000 snake species)2,3,4,5. In contrast, the lizard venom system is thought to be restricted to just two species, and to have evolved independently from the snake venom system1. Here we report the presence of venom toxins in two additional lizard lineages (Monitor Lizards and Iguania) and show that all lineages possessing toxin secreting oral glands form a clade, demonstrating a single early origin of the venom systems in lizards and snakes."
Fry BG, Vidal N, Norman JA, Vonk FJ, Scheib H, Ramjan R, Kuruppu S, Fung K, Hedges SB, Richardson MK, Hodgson WC, Ignjatovic V, Summerhayes R and Kochva E (2005) “Early evolution of the venom system in lizards and snakes.” Nature doi:10.1038/nature04328 (onliine 17 November 2005).
Heloderma species aren't the only venomous lizards. Even wikipedia knows!
In late 2005, University of Melbourne researchers discovered that Komodo Dragons (Varanus komodoensis), Perenties (V. giganteus), Monitor lizards, Iguanians such as Pogona barbata may also be somewhat venomous. Previously, it had been thought that bites inflicted by these lizards were simply prone to infection because of bacteria in the lizards' mouths, but these researchers have shown that the immediate effects (at least in the Komodo Dragon, Spotted Tree Monitor, and the Lace Monitor) are caused by mild envenomation.[1]
Mexican Beaded Lizard - Wikipedia, the free encyclopedia
so as for the bearded dragons, looks like another Pogona species could have slight venom.
Thanks for the clarification! 
