Web Based Backend Systems

What kind of products can I use to run the back end of web site to provide interactive services to customers?  How can it be exposed so my customers can interact with it?

Interacting with Leads / Customers

Once I get a customer or potential customer to my website, what do I do next?  This is a huge topic and could explore areas such as lead tracking and providing customers the correct information they are seeking.

Search Engine Optimization

OK, I've got this website, so how do I get people to find it? What are the techniques I should use to make sure that whenever someone does a search looking for what I'm selling, they can see what I'm offering?