I have purchased 300000 baseball cards. Yes thats "Three hundred
thousand" cards. Does anyone know of an automated software package
that I can use in conjunction with a scanner to [catalog] all these
cards. In a pefect world I would like to have them made availiable for
sale via an online store.

There are programs that allow you to catalog your baseball cards, such as:

http://www.itlocation.com/en/software/prd40305,,.htm

but I would doubt that there would be a fully automated system as
baseball cards don't have bar codes - you can't scan them in the way
you can scan books, etc.

I would also venture that many of the cards are virtually worthless -
it might just be better to identify the valuable ones.

I hope this helps.

Have a good day.