http://www.carpet-rug.org/index.cfm
Carpet and Rug Institute, good general information.

http://carpet.iflooringinfo.com/
Carpet oriented, but lots of good, well organized area rug related information.

http://www.carpetbuyershandbook.com/
Another carpet oriented site, but wealth of rugs related information as well.

http://www.greensage.com/SLCP-FLOORING/SLCPcarpeting.htm
Some information on the environmental impact of carpeting.

http://www.nps.gov/sustain/spop/carpet.htm
About environmentally responsible carpeting choices; partly relates to area rugs.

http://www.shopsicle.com/articles.php
Informal but interesting, lively site with quite a bit of practical information.

http://www.the-home-improvement-web.com/information/area-rugs.htm
Rug purchasing tips...

http://extension.usu.edu/files/homipubs/hi05.pdf
Utah University article on carpet and pad selection; good reading.

http://www.afcee.brooks.af.mil/dc/dcd/interior/indespubs/carpetselecthndbk.PDF
Another very informative overview of carpet construction, materials, styles, etc.

http://carpet-cleaning-links.com/
Carpet care and cleaning - very informative site.