I have tried out various carts and I know different people will have different opinions, but I myself settled on Zen Cart.

Why?

- The software itself is excellent, and fairly easy to use.
- Continuous security updates release promptly when necessary.
- The support network available at www.zen-cart.com has always been helpful
- Third Party companies creating excellent plugins and extras
- IT'S FREE!

...The list goes on.

I found this link to a good Zen Cart installation guide, should it be needed:-

http://tutorials.zen-cart.com/index.php?article=107

Want an example of a Zen Cart installed shop? Check Out Here.