I recently began using the Office Ally clearinghouse and it is GREAT.
FREE for all commercial carriers. Flat fee of $19.95 per month if more than 50% of your claims are governmental. I enrolled and was submitting claims in 2 days. It was easy to set up, they logged in to set it up with our PM software. Nothing to install on your system, it is web based. If your PM software can print a claim, you can use OA. They extract a text file, then convert it to the 837 format to go to the insurers. Send all of your claims in one action versus individually to insurers.
A la Wendell, did I say it was FREE?