The Two Fat Lardies set Through the Mud and Blood is very good.
1 model = 1 man and it normally handles games from with a platoon to a weak company a side. It really brings out the late war small unit tactics with specialist rifle grenade, bomber, trench clearing and LMG squads.
They do a scenario book on the western front and the first few scenarios are directly taken from training manuals of the periods. There are also additional materials in the summer/winter specials they publish,including special rules for trench raiding
You can find battle reports and more ideas on trench raiding games in on Sidney Roundwood's excellent blog "roundwoods world".