I would safely say fishing village for $3 is one of the best! Otherwise usually just treasures, other than fools gold and talisman 
I agree with Fishing Village. I find it more often bails me out of drawing two jacks then it clogs me up by being blind drawn with no actions left. Possibly this is to do with the duration effect.
Lighthouse also seems to work well with a two Jack deck, I've found.
Other possible contenders which I am as yet not sure of are Crossroads, Native Village, Inn and Governor
For your consideration: Native Village and Governor with double jack on solo game, 4 provinces by turn 12:
http://dominion.isotropic.org/gamelog/201201/25/game-20120125-021029-0c6f4527.htmlHaving said that, on solo games you can of course use Governors alone to get 8 provinces in 11-14 turns...
Mostly this is from solo practice games, but I've found that Jacks + either fishing villages or lighthouses hits four provinces faster than just jacks.
As for Remake, Chapel, Loan, Moneylender or any other means of trashing coppers with a terminal or treasure, I'd agree its just too slow. A single Upgrade, on the other hand, seems to work fine, though there's always the problem of what you trash silver into when you're forced into that corner (as the deck kind of requires you to hit the Upgrade even if its done blindly). The window for me buying upgrade is pretty narrow though (both Jacks already, exactly $5, and too early for duchies), and I'd defy conventional wisdom by saying that you should upgrade estates over coppers preferentially, as that does more for your average$, even if Jack can trash those estates when it can't trash coppers.
A single Lookout, I think is actually pretty solid with Jack. Being a card down hurts less when you draw it with Jack, and between it and Jack you can pretty much guarantee that the first card you draw back is going to be decent.
Oh, and then there's the obvious combo with Jack... Gold!