Help! Which shopping Cart and User Registration Solution should i use?

[winvest]

What is the best/simplest user registration + shopping cart solution out there right now?
Here's what I want to do with it.

I want my customers to do 5 simple steps
1)Register
2)Login
3) Fill out contact and shipping info one time only (so they won't have to do it ever again)
4)Add items(or service) to a cart
5)Checkout

This is a equipment repair service website.

My goal is for customers to submit info about a specific device they need to have repaired into a "Service Ticket", then make a payment selection based on their repair request(Overhaul or Estimate), and then checkout. After the payment, they Print out a "service ticket" and put that into a box with the equipment to be repaired and send it in.

The next time they come back they don't have to fill in contact info or shipping info for the "service ticket". that information will automatically populate the ticket. all they do is specify the type on repair and checkout.

The solution i'm looking for should be turnkey, and customizable w/o any coding skills. Just like google apps.

What do you guys think?

Thanks in advance.