OT: Shopping cart recommendations wanted

[Larry Cook]

I'm looking for recommendations on shopping cart software.

My dad has asked me to help him add a shopping cart to an existing web site. 
His hosting service offers ShopSite and Americart, but neither of them can 
support the convoluted shipping and insurance pricing tables used by the 
client.  This means we need the ability to write our own shipping and 
insurance computation code.  The hosting service also supports CGI, Perl5, 
PHP4, and MySQL.

There seems to be a lot of software out there ranging from very basic shopping 
carts to more broad e-commerce platforms.  I'm hoping that some of you can 
narrow the field for me so that I can concentrate my time on evaluating only a 
handful instead of the slew I'm finding.

Thanks,
Larry