The First One : OneThousandPaintings
Idea: Numbers from 1-1000 are painted and are painted only once. So the numbers already ordered are gone. There are still about 227 paintings left. And these paintings are not cheap either. The price is 1000-number. But people are still buying them like crazy, read this excerpt from that website's blog:
Tosh Cooey, owner of 314, 159 and 265 (that's right, your reaging PI, i.e. 3.14159265) wants to expand his series and is looking to buy 358 and 979 (because PI = 3.14159265358979). If you own them, he offers USD 500 for each.Best of all, people are reselling their paintings and claiming upto USD3300$ for it. The artist who came up with this idea is Sala, a Swiss artist. And btw, she also has made an applet where you can see the DOM structure a page visually using cool tools. You can check it out at : http://www.aharef.info/static/htmlgraph/
The Second One : 365SpecialDays
Idea: Inspired by the previous one, in this page, people can submit a day that was special to them and why it was special. Based on this, the artist will paint a picture and mail it to you. All of it comes for about 182.5$ (the reason for such a price is because it is half of 365). Only 365 paintings will be made, if your day is gone, you wont get it back. Artist behind this venture is Fernando.
Lastly, there is an excellent compendium of visualization tools which can be read here.