I’ve recently run across an interesting website which collates a bunch of submission calls so you don’t have to do quite as much searching on your own. Obviously, at this late time of the month, some of these deadlines have passed, but I get the sense that this list updates monthly. I should also say that this list is hardly exhaustive, but it will get you on your way.
If you have other links to similar clearing houses, please post them here in the comments.
Best of luck!