Gaylen,
There are many choices out there for sure, but dealing Merchant Providers can be a painful experience.
My personal choice and what I recommend to my customers is Authorize.NET and a company called MerchantPlus (
https://secure.merchantplus.com/20).
While you there are many providers - and I've gone through 5 different ones by now - MerchantPlus has been outstanding in terms of getting accounts hooked up and running within a day and providing customer support beyond the call of duty. The latter is something that I've never seen in countless dealings with merchant companies both personally for my site as well as those of customers...
Basically with Authorize.NET all you need is a simple HTTP POST interface to send payment info to a Web Server... it couldn't be much easier.
+++ Rick ---
>My client needs the ability to allow a customer to make a quick payment on for an invoice about to go past due. I know there are phone and internet solutions. Anyone find one that is good and doesn't have too high a transaction fee. This is really only for a periodic payment and not a bill pay type solution.
>Thanks in advance
>Gaylen