There are enough cartooning gigs appearing online these days that I can no longer keep up with them, although I’ll keep trying… there is a list on the top of the site (and the left side of the home page) of things I’ve heard about and got around to adding, and we have a section of the message board here that anyone can post their opportunities to. Fortunately there are other places to check as well!
Conspirator Andrey Feldysteyn does an excellent job keeping up a list of cartooning opportunies, with a focus on international cartooning and gag comics competitions (among other things).
The Comics Journal message board has frequent opportunites that pop, particularly for the small-press cartoonist:
The Digital Webbing forum used to be a good place to look for more mainstream comic book industry gigs, although I don’t see much of that there these days glancing at it.
I’ll post more of them here as I run across them… please post others on the message board here if you know of them!