Currently there is only one Artificer Prestige class, the Battle Engineer, and while it is certainly a strong one I'd like to see some more. From the second I saw the Construct Essence feat I knew I wanted to see the Self Forged prestige, and I think It deserves to not be written off by one feat.
Here's a link to the Self-Forged:
Basically I envision this prestige to require construct essence, and it would further increase the construct essence feat until eventually you are no longer able to be healed, have x% fortification, have warforged immunities, immunity to sneak attack damage, repair for 100%, and is considered a construct (you can reconstruct them, use reinforce construct on them, etc.).
Self Forged replace their arm with a battlefist (is a part of the Mace weapon group, and has a +3 enhancement) The Player Character can still wield a weapon in their battlefist instead, but can't use their battlefist abilities.
I'm not entirely sure how to work the battlefist in, but my guess would be to give the artificer an unarmed strike of 1d8, and allow them to augment their fist (instead of hand wraps the slot would be vacant).