listHD.com allows users to post HTML ads with three large image gallery options to craigslist. The end result is a craigslist ad that stands out with better styling and nice image options. Images uploaded to listHD are saved at 1000px instead of 300px.
The process for posting is pretty easy. First, users register at listHD.com. Once registered, they post their item on listHD with photos and possibly embed a YouTube video or two. After their listing is posted, they can select between the two different image gallery templates to generate the needed HTML for their craigslist ad.
Of course use of listHD is free, so users have nothing to lose and a great ad to gain.