If you are looking for another company to check out, I suggest that you look at Digital River.
Beyond Digital River, PayPal, and Google Payments, I am sure that there are other companies for this. Just remember to take a look at the possible implications as you choose you payments processor.
I believe that the problem you will run into if you go with a smaller or lesser known service is going to be one of inconveniencing your customer. If clients already have a PayPal account as millions of people do, buying something from merchant that takes PayPal is pretty easy and relatively secure.
If you go with a lesser known vendor for your payments, you have to then deal with the implications of clients having to decided whether to trust your site AND whether they want to trust the folks that are processing your payments. Additionally, your clients may have to create an account with the folks that are processing your payments. If this is the case, you are going to lose sales as folks browse away and look for an easier option.
Personally, I tend to be a bit guarded about what sites I am willing to buy from. Often I feel more comfortable paying a bit more from a site that I trust, as opposed to running the risk of handing my credit card info out to someone that I am unsure about.
And I am sure that I am not the only one that shops on-line this way.
