From what I can see, the Chancellor (base set; allows you to immediately move your deck into your discard pile) coupled with an extra action and the Harbinger (Dominion Update Pack; allows you to take any card from the discard pile and put it into your hand) could make a pretty fantastic combo, giving you any card from your deck (as well as giving any reason to use the Chancellor). Is this a viable strategy?
This doesn't work as you are thinking:
Harbinger has you draw a card before you look through your discard pile. This means that when you play Harbinger, the first thing you do is draw a card, which requires you shuffle your discard pile and make a new draw deck. So having played Chancellor first actually makes Harbinger worthless!
Harbinger doesn't put the card into your hand like you said, it puts it on top of your deck.
Because Chancellor is a terminal action, and would need to be played before Harbinger, this requires that you first play a Village or another action that gives +2 Actions.
Even if it did work as you were thinking; the end result would be the 1 best card in your deck gets to get played sooner in the shuffle rather than later; or maybe played multiple times within 1 shuffle. This same thing is accomplished with both Scheme and Scavenger by themselves; instead of requiring a multiple card combo.
A minor point, but as Chancellor was removed from the second edition of Dominion, which is where Harbinger comes from; these 2 cards don't both exist in the same "Dominion world". Of course in casual play they are still both available; but it's likely that online play and tournaments won't have them both.
The Chancellor + Harbinger combo is useless because of the + 1 card effect of the Harbinger, but if you're looking for a very similar effect, try using the Scavenger from the Dark Ages expansion. With it "you may put your deck into the discard pile. Look through your discard pile and put one card from it on top of your deck." - Also + 2 money.