I need to accept payments from the premium account holders on my website through VISA/Mastercard Credit/Debit Cards & paypal. Is there any well known widely used API that can make my life easier by abstracting all these payment procedures?
IP*Works! from nSoftware has a good toolset: ICharge Payment Integrator
However, unless you are fully prepared for the nightmare that is PCI compliance, just use Authorize.Net or PayPal's standard methods. What they charge you in fees you will be more than happy to pay compared to what happens if you lose credit card numbers to hacking.