A short list of popular compatible merchant accounts:

It is by no means, a comprehensive list

Costco, NOVA, Bank of America, Paymentech, Cardservice International, Bancard USA, NPC, Total Merchant Services / TMS, Merchant eSolutions, Humboldt Merchant Services, North American Bancard / NAB, ECX, Ecommerce Exchange, US Merchant Systems / USMS, Wells Fargo, Retriever, NxGen, United Merchant Services, Norcal Cardservice, Cornerstone Payment Systems, Charge.com, CDGcommerce / CDG Commerce, Millennium Bankcard, Echo, iPayment, Online Data Corp / ODC, Innovative Merchant Solutions, Chase Merchant Services, Partner America, Data-Link, Money Tree, First American Payment Systems, EVO, MSI, Cynergy Data, Signature Card Services, iTransact, First Data, Global Payments, Concord EFS, MerchantAccounts4Less, PaySystems, Payment Processing, Practice Pay Solutions, Advanced Merchant Services, CC Integration, CSI Mid-South, Authorize-IT, CyberAuthorize, eCom Merchant Solutions, Global Payments, Internet Media Solutions, Internet Commerce Consulting, Merchant Accounts Express, Hometown Merchant Services, Merchant Plus, Merchant Warehouse, MCCS – New Jersey

Gateways that you may be upgrading from:

AccessPoint, Bank of America, Bluepay, CDGGateway, Cybercash, DPI Merchant Services, ECHOnline, ECHO, Inc., eConnect, EFT Secure, eProcessing Network, EFS.Net, Ezic, goEmerchant, GOrealtime.com, iBill, IC Verify, Innovative Gateway, Intellipay, Iongate, Itransact, Linkpoint, Lynk, NobelPay, Orbital, Paradata, PayJunction, Pay-Me-Now, PaymentProcessor.net, PayPal, PayPal Standard and Website Payments Pro, Pay Quake, PayReady, PaySystems, PC Charge, PSI Gate, QDebit, QuickCommerce, Rich Solutions, RT Ware, SecPay, Securepay, Secure Source, Signio Payflow Pro, Skipjack IC, Surepay, TakePayment.com, Terra Payments, The Processing Network, TotalPay, USA ePay, Usight, Verisign, Verisign Payflow Link, Verisign Payflow Pro, Virtual Money, 2CheckOut, and many more