Can you be more specific? Your own product or product of others (just promoting)? Physical products or digital products?
If I understand your quey correctly, you have some type of software application and/or IT service? It really depends upon what you are selling and to whom.
Well... A program for selling on the internet is Google Adwords. But that answer is about as valuable as saying that a scalpel is a tool for surgery, and expecting someone to be able to remove an appendix with it. Pay Per Click drives the quickest traffic, but can be expensive. Do some research on this forum and elsewhere.