Authorize.net and 2checkout.com are pretty much the dominant market players. I realise you said not PayPal, but in case you are not aware PayPal does offer credit card procesing for standalone websites independent of eBay.
Often your best bet is going to your own bank. Most have commercial accounts and cc processing available. I use my business' bank for both offline and online processing, and PayPal for new/experimental stuff plus eBay sales (I use PP for new stuff and stuff I'm only testing out because it's the easiest and fastest to set up -- you just add the new payment address to your account and go.)