And forgot to add, the German 210!  The really big heavies (12", 305mm, 420mm, etc) are nice as well, but seldom close enough to the front to be added as on-board artillery, except in the largest games.

Some German 210s would be great, too- much bigger than that, and it's mostly off board anyway!

We do have some more WWI artillery pieces in the pipeline and some vehicles later in the year.  Can't give you full details yet, but they won't entirely disappoint.