I was working on the Artificer myself the other day (and of course it's at home, so I don't have it in front of me.

). Basically, I bumped the HD up to d8 and shuffled the order the craft feats came in (Forge Ring is available at 7th level in Pathfinder, and there are other less extreme adjustments as well). I was pretty happy with the feat order, spreading it out over the first 12 or 13 levels. After that it's empty at the moment with the exception of the bonus feats.
On one hand, that doesn't completely bother me, as the Eberron campaigns I have in mind will all end before or right around there. On the other hand, I'd like to flush it out for my inner completist. Does anyone have any ideas what would be useful for higher level Artificers? I'll take a look and see what Doug Anderson's Northern Crown gave to the Natural Philosopher class at high levels, as that might be a good match.
Another issue is the Craft Reserve. As the XP component for crafting magic items goes away, this needs adjustment. I was thinking of just converting the XP reserve to a gp reserve worth 5x the current XP value, but it looks a little....underwhelming. Needs more thought. Perhaps a 10% reduction in cost every 4 levels?
3.5 artificers are pretty much broken. A 3.5 artificer with one or more warforged in the party is pretty much game-breaking in my experience.
Shazam, would you expand on that a bit? I'm curious what the problems you saw were.
I've been thinking about this a little myself. I would use the spell table of the Bard for the Artificer starting with 1st level infusions = 0 level spells. I think most of the 3.5 Eberron rules will transfer over easily. Basically, low at the base stats and bonuses for the Bard as a guide and I think you'll be okay.
Collin, why do you think the Bard spell progression is better?
One question I have: if a super 20th level special ability were added to this class, what should it be?
I'm not entirely sure it's necessary. The Cleric and Wizard don't get one.