The Samnite spearmen you can recruit in southern Italy are great javelin fodder I've found since their armor seems to do a good job protecting them long enough to attack, unlike a principe or triarii. In fact before I started facing huge gallic and germanic stacks they played a very large role in all of my armies as the rebels that constantly spawned were all javelin users. Problably the sole problem with them is that they don't have that 'fight to the death' instinct a good roman has, and often will rout if their fighting alone.