They offer everything the big dogs do, but their staff is incredibly helpful and attentive. We use them on FamSpam and GitHub.
I wouldn't find the merchant with the lowest rates, find the one you like the most. As your business grows, you can always renegotiate your rates.
http://www.braintreepaymentsolutions.com/truth-in-pricing-gu...
You may have to shop around to find a payment solution that fits your business. Just a heads up.
http://groups.google.com/group/rails-business/browse_thread/...
And when you do get a quote from someone, use this tool to rate it:
http://www.quotesignal.com/merchant-account-comparison-calcu...
EDIT: I know it's bad form to complain about downmods. This isn't a complaint just a statement that I'm flummoxed as to why this would be voted down.
I try to make decisions relatively quickly when the consequences are mild for a sub-optimal solution so that attitude sold me.
Highly recommended: http://www.dharmamerchantservices.com/
Sorry about being hush on the details, I'll let you guys know it all soon. ;)
Authorize.net is a bit pricey and a bit difficult to use. But, it is the gateway service that we currently use...and when I switched to another shopping cart, we didn't have to change gateway providers or write new processing code. Which was nice.
When we write our own shopping cart (which seems impossible to avoid, because everything we've tried is such a poor fit for the way we sell our software), it won't tie into Authorize.net. It'll use PayPal, Google Checkout, and some other payment gateway (whichever one works with the cheapest merchant services provider, while still offering recurring payment support, probably).
Also, I'm surprised that ProTX ( http://www.protx.com/ ) hasn't been mentioned on this forum. Anyhow, whatever you pick, it'll probably be cheaper and more responsive than WorldPay.