I'm looking for a shopping cart script that is built for downloads.

I want to integrate it into my site, so it should preferably be easy to integrate.

It must be able to sell downloads, and integrate with PayPal.

Suggestions?

Not sure what you existing site is, however, if you have some joomla installation you could use VirtueMart, wrks perfectly with downloads and tons of extensions are available too....

I would suggest Joomla/VirtueMart too.