I need to install an online shopping cart, that my clients can update themselves online. They will not be able to work on the site, just add their merchandise. Does anyone know of any software that I can use for this? I'm currently using Paypal that I put on the site, but would like for them to update the shopping cart without my help. Also are there any free or real inexpensive programs out there?

Try osCommerce...it's an open source shopping cart with a great track record. I'm not sure if they allow Paypal yet because Paypal is a little new to the merchant account business.

Actually OsCommerce fully supports PayPal. A site I did over a year ago takes payments that way.

OsCommerce is very good, has many extensions and themes, and supports Paypal very well. I would also recommend CubeCart, which is also free to use (they require some $ to remove the copyright link) and is also very good with Paypal, and can be setup for client store maintenance.