We started using Merchant Cost Consulting earlier this year. These guys are former banking and credit card reps who go and negotiate your processing rates on your behalf. Now, like most of you, we are pretty aggressive about shopping our processing rate around, so I wasn't sure they would be able to save us much money. Boy, was I wrong.
On average they are saving us $600 per month. The deal is we split it 50/50 with them for so many months, after that all of the savings are ours to keep. Plus, they keep an eye on your fees during this time to make sure those @#$% credit card processors don't find a way to jack up your rate again.
They are good folks, and they actually do what they say they do. Actually, in our case, they under promised and over delivered. They estimated $500 per month in savings, and it's been closer to $600.