Re clubs:

Psycho is absolutely right. The club or cudgel, when made out of wood or otherwise, is a surprisingly effective weapon.

A blunt force weapon is not about the material used, but about the weight involved. Probably the most damaging historically speaking are the Arab 'amud or the Nubian basalt-headed maces. There are firsthand accounts of 'amud weighing 10-15kg (yes, that heavy), and also crushing helmeted heads into a lopsided bowl full of brain soup.

From testing maces vs. clubs on various types of armor, metal or otherwise, I can tell you that clubs are about .03 less effective than most mace types, excepting flanged maces of the East Greeks and Parthians. That is to say, they managed to defeat armor and 'kill' the wearer a significant percentage of the time.

I'm not sure I know enough about the topic to argue as eloquently as Psycho has here, but I would like to add one bit. Written sources will always favor the Romans, because they, umm, wrote them. Archeology has only just begun to unravel the complexity of Celtic society and warfare.

Psycho: as far as Cunliffe is concerned, a (albeit much truncated) Boii kingdom existed until about ~100 A.D. Are you disputing that? I'm a bit confused, I would like a clarification of your point where you mentioned the defeat by the Dacians.

Btw, Anthony is quite right about the Germanic vassals of the Boii, at least with regard to current scholarly opinions. Excavations in Austria and Czech have confirmed large amounts of tributary items of Germanic origin at the sites of principle Boii-controlled Oppidae concurrent with the layers precisely dated with contemporary Roman pottery. This in itself (the very abundance of items) is as good an indication as any with regard to tributary payments.

Further, the very expanse of the dated areas mean that the Boii of central Europe controlled a vast area at their height.