The latest 105mm used by the US is the M119. The AFV Club M102 is still in use by some National Guard units. I know the Mass. ARNG still bums some parts off of a pair of mine that are inop.
If you don't want towed arty, Italeri does the M109A6 Paladin. It is also boxed by Revell. In fact, just about every variant of the M109 is boxed by either Italeri or Revell (all basically the same kit).
Revell also does the German Panzerhaubitze 2000 that comes with a huge aluminum barrel.
The older M107/M110 is also put out by Italeri and reboxed by Revell. It served in the US through Desert Storm.
One of the US/NATO's most modern artillery pieces is the DML MLRS and MARS (NATO variant).
Hobby Fan also made the towed Lance missile. It was used by the US into the late 80s/early 90s. I think they did a conversion for the tracked variant as well.
Heller does a couple of 155mm SP howitzers based on the AMX-30 chassis.
Trumpeter also does some Chinese SP artillery pieces.