I submitted my first ever piece of tanka prose (which is like haibun but with tanka instead of haiku) to Haibun Today last week. This was my submission for week 15 of 2011. It was my first time submitting work to this on-line publication, edited by Jeffrey Woodward, with New Zealand's own Pat Prime as Assistant Editor.
I received a quick email reply from Jeffrey, which was unfortunately a rejection, but a very encouraging one. And I will be submitting work here again in the future. You can find the submission guidelines here, and lots of helpful articles and interviews here. And don't forget to check out the current issue!