As I have stated many times before, I'm an achievement junkie.

I had a week holiday over xmas, and all the time I played diablo it was searching uniques. Hunting down a single unique can be a task of several hours, and can become quite painful. Especially if you need one in a random-generated map.

The point I actually want to make is that a lot of money can be made hunting uniques for guys like me.

On the EU forums I discovered a bunch of posts under the "quests" tab where people post their missing uniques, and what they are willing to pay to get them. I'm pretty certain on the US forums you will be able to find something similar.

Obviously some of the uniques don't count. So it helps to keep an eye on the "Unique Collection" achievement to see which uniques people might want.

And just as a side note. A lot of the Act 3 uniques are on the route that people farm endlessly.
For example I still need 2 uniques in Arreat Crater 1, and one unique from Rakkis Crossing, and one from Skycrown Battlements.
All areas that forms part of some people's normal act3 farming runs.

I posted my list there as well, and it saved me hours in hunting down the uniques myself.

I'm currently about at break-even in terms of money.
I have bought about 8 uniques at 2.5 mil each.
But each time you actually run into a unique you can sell it to up to 3 people at once. And on EU server people pay between 500k and 5 mil per unique find. (Average seems to be about 2M)

Yesterday I was even in a game with a guy offering 20M because it was the last unique on his list.

So bascially what I'm saying is this: if you run into a unique, even on your normal route. Take 5 minutes to check out the forum to see if someone will pay to come and kill him. It helps out the unique hunters if more people are aware of this, and it helps out everybody else to make a little extra money.