Self-propelled artillery:
1.)
Panzerhaubitze 2000 [Germany]
This thing is a kickass piece of machinery. It can let loose quicker and farther than any other self-propelled gun, and has the best computers out there. Many armies are looking to Germany to replace their aging M109 howitzers.
2.)
M109 A6 "Paladin" [United States, NATO nations, Israel, plus many others]
It is the final evolution of the M109 chassis, and though it is nearly forty years old, it's still kicking ass. As I said, it is being replaced by the Phz 2000 because it fires faster and is much more up-to-date.
3.)
M270 MLRS [United States]
I assume we may include MLRS systems in self-propelled artillery? This guy is basically a mobile missile battery, with huge range, huge destructive power, and of course uses guided munitions. I don't think it's as good as the two before it because it is an exclusively long-range weapon, and carries pretty much zero protection of its own. They're not supposed to, but in a real pinch you could use mobile howitzers as tank destroyers (indeed, that is partly how self-propelled artillery came to be so widely used in WWII), or at least as armored fighting platforms, since they also carry .50 caliber machine guns and respectable armor.
4.)
TOS-1 [Successor states to the Soviet Union]
This is a Soviet-designed MLRS system designed for much closer targets than the M270 envisioned. The weapons the TOS uses are mostly thermobaric anti-personnel warheads, and are for the most part unguided. Think of this almost as a super "Katiusha" system. They used them with relative success in the Afghan War, though they entered very late. I think they were also used in the Chechen War.
5.)
PLZ-45 [People's Republic of China]
This is another 155mm gun, relatively new, but its just not as good as the #1 and #2 slots. It fires a bit slower than the M109, and much slower than the Phz 2000, but is in general a good piece of equipment. The Saudis field both the PLZ-45 and the M109.