What is the best cart or cms system for selling intangible product such as unique number.

Example: Customer places a order
Email is dispatch instantly after payment verify with order information,instructions and a unique number.

Every order will be a different unique number not the same so can't be one of those audio download module or such.

please advice the best cart system and or CMS that is fully customizable.

Thank you in advance.

try Oscommerce, Avactis, zencart
they're open source or some fee
every site has demo versions, check them out!

There are many shopping carts out there. Look around and see what features you can live with out and what features that you absolutely have to have.

oscommerce has many modules. you can find something that would fit to specific gig youre gonna operate.