It's very difficult to get a publisher to accept art from an artist outside their established stable. Not impossible, but difficult. I know that some agents (Elena Roth for one, IIRC) work with writer/illustrators and sell their projects that way, but beyond that you have to have something spectacular.
I've had artwork up before editors at two major houses, and with the one of those two that thought it was "Adorable", they didn't think the story was right (the other house said the same thing, only with the words reversed for art and writing) so it's really a matter of hitting a perfect balance - which is infuriatingly hard if you're set on illustrating your own stuff.
I've put a couple of things on my blog, but not many. I'm more protective of even my rough drawings than I am my writing.