If you're building or re-building a website I'd highly recommend using a Control Management System like Joomla or Drupal. Here's some advantages.
* They're Free
* They're constantly being developed and improved on.
* you can get them to look how you want easily as they built in MVC - making the website easy to skin and changed layouts.
* Excellent community tools.
* Add components to intergrate your website with Twitter, Facebook and other social media website.
Drupal vs Joomla
Reading from several blogs on this topic it's pretty obvious it's a close run thing. And really depends on you skill level and what you want to achieve. Drupal has apparently a hard learning curve and out of the box can be a bit lacking. However once you get into the framework it's the powerful.
Both have Shopping Cart solutions that can be added. Due to having more experience with Joomla I more often than not would pick this as my tool of choice.
Please feel free to leave comments and links on more blogs and thoughts on this subject.