Some products mark on the box if it work with Linux:http://www.linuxjournal.com/content/linux-label
Creative Live Cam do it to, so easy to buy them if you using linux:http://www.creative.com/mylivecam/products/product.aspx?catID=1&pid=19008
But I wonder why printer manufactors don't do it? Even printers known to working with Linux drivers that "works out of the box" have no label with it.
The only ways seems to go on their homepage to look at the specifications:http://welcome.solutions.brother.com/bsc/public_s/id/linux/en/index.html
When I looked at a Samsung ML-1640 (good price at that time) it was no information about Linux on it. The people at the shop could not answer or know anything about Linux.
So I must go and look here before I bought it:http://www.openprinting.org/printer/Samsung/Samsung-ML-1640
3 penguins fine. And it work in Pardus, Ubuntu and all the other Distributions I have tryed.
But how easy it would be if they just put the "Tux" symbol or just write "compatible with Linux" at the box.