Self-Propelled Guns have gone on to see standardization in many militaries around the world, each system capable of sustained fire rates of conventional or nuclear-tipped warheads. Today, every major national army fortifies their respective armored divisions with a healthy collection of self-propelled artillery systems. Systems on order heading into the new year are NOT taken into account.
SPG strength data through 2016.
Sources: CIA.gov, CIA World Factbook, wikipedia.com, public domain print and media sources and user contributions. Some values may be estimated when official sources are lacking.