From what I have heard on other sites, Mike Holt especially, SM is to be avoided at all costs. Terrible customer service and you have to fight to get lead fees credited whan there is a problem.
Bidclerk.com seems to have more commercial type work, at least in my area. I have no experience with them.
Contractors.com has a lead service but seems to have very few in my area.
You may want to hop over to the Business forum on this site and do a search for other ideas.