There really is no software that will do it consistently. You'd be better off paying for an experienced poster who knows their way around Craigslist
I'v heard of someone offering that kind of services on here, but i didn't like their prices. So it makes 2 of us who is interested in this tool
Have guys taken a look at patmiller27.com... Good tools there for CL marketing. And above all, our software applications really DO work!
How often do you need it posted? You can make a script do it, its pretty easy. Sometimes craigs throws in a wrench or two, but its not too bad. LMK if you need more help.