CRITICAL NETWORK (UK)
This site has a small number of really good submissions. My best exhibition that came from this site was a group show in Poland. I was flown there, put up in a hotel, fed, and attended the opening at a major cultural institution. An all expenses paid exhibition. Did I mention they also paid for my installation art piece to be manufactured and paid for?
This is a massive site with so many submission deadlines it can be overwhelming. But they also have a lot of on-line resources for artists. They have deadline lists for each month plus a list of rolling deadlines. Also included are residencies and so much more.
THE ARTERY (Canada)
http://www.britanniacentre.org/services/arts_and_culture (click on pdf)
This is a big submission list in Canada. Excellent and includes residencies and international submissions.
http://www.mallgalleries.org.uk/call-for-entries (UK - good idea to join their mailing list for deadlines)
http://calendar.preview-art.com/calendarcategory.php?id=Opportunities (Canada/USA-west coast)
Mailing lists of submissions (Canada)
http://www.instantcoffee.org (go to Contact and apply for your region of choice)
If you know of any more good submission lists, leave a comment with a link, and I will add the comment.