http://escapadecon.net/
http://2012.arisia.org/
http://www.bf4f.org/
http://www.hp2012.org/
http://artshow.dragoncon.org/index.html
http://www.wiscon.info/artshow.php
http://www.katsucon.org/exhibits/katsucon-17-art-show/
http://www.conceptsff.ca/2011/art2011.html (artist or agent of artist must be present at this con)
http://www.ad-astra.org/?page_id=244
http://www.vcon.ca/what/art-show
http://www.westercon64.org/?page_id=219
http://www.spocon.org/artshow
http://www.fanime.com/art/#art-gallery
http://www.megaconvention.com/
http://www.sfnorthwest.org/ (pacific northwest sci-fi con listing)
http://www.conventionscene.com/ (comicbook convention listing? I haven't taken a close look yet)
this is just really cool and I wanna put it somewhere:
http://www.bleedingcool.com/2011/08/03/joe-quesadas-hyper-detailed-fantastic-four-50th-anniversary-artwork-tutorial/