If you're in Canada and looking for plastic bags/sleeves for steelbooks/cases, give blankmedia.ca a try.
http://www.blankmedia.ca/DVD-OPP-PLA...-Prodview.html
$3.25 for 100 14mm resealable bags. They're fairly thin, and will work just fine for normal steelbooks, and are alright for blu-ray/ps3 sized steelbooks. Not recommended for steelbooks that have any sort of sleeve already on top of them.
As for the site, they're great for anyone who's in Ontario since orders can be picked up to eliminate shipping costs. They also sell replacement cases for PS3 game cases for $18.95 for 46, and 360 game cases for $18.95 for 54.