Out of the gateways mentioned in this thread, my vote would also go for Authorize.Net.
Just remember that there are two pieces - the merchant account and the gateway. Authorize.Net or Verisign or Linkpoint is the gateway... you still need to have a merchant account to authorize you to process credit cards. The good news is that usually these are offered as a bundle through various merchant processors so you can get them both at the same time.
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