As soon as i discovered HDRI lighting, i jumped on my keyboard to find all the free HDRI ressources i could on the web, so here are some links:

http://www.hdrimaps.com/downloads.html

http://hdri.3dweave.com/library/ here there is a lot of hdr

http://www.aversis.be/extra_hdri/00.htm they are a the top of the page

http://www.evermotion.org/index.php?unfold_exclusive=84&unfold=exclusive some hdr skies

http://www.digitalin.fr/index.php?page=goodies the link is under the teapot pictures

http://www.debevec.org/Probes/ here are some hdr light probes, but you have to unwrap them using HDRShop

http://gl.ict.usc.edu/HDRShop/ free HDRShop program, you have to fill the form to download it

http://www.hdrmill.com/Freebies.htm

http://www.spectralogue.com/textures/index.php?path=50 very great quality, some other textures also

If someone else has other links, feel free to share them, as you never have enough HDRI maps to play with ;D

My Store