Places to buy very cheap CDROMs containing common LinuxDistributions:
Some sources of CDROMs donate money to OpenSource charities and some don't, check their web sites for details.
When you buy from such sources you are effectively paying for the media and shipping, almost always the CDROMs are created from ISOs which you can download free of charge. You also get no support. Note that even when you buy direct from the vender you might get no support, read the fine print. A good places to download the ISOs or other forms of linux are listed in NewZealandLinuxMirrors (at least if you're in NewZealand).
No other page links to IsoCdVendors yet.
AllLinuxCD.com