I am looking for eCommerce solutions that supports Customer Groups for:
a.) The ability to secure and custom price products by Customer Group and associate users to the group(s).
b.) The ability to setup secure 'Customer Stores' (we are a custom embroidery shop) that allows a user to only see the products that they have agreed to sell(typically to employees) with photos showing the products with their company logo on them.

What solutions, if any, are people currently using to provide this type of functionality and is it out-of-the-box or custom built functionality?

Thanks for your input.

Its unlikely that you will find a solution that does both.
IMHO you will need some customization to make this work with solutions such OScommerce.

I know CRE Loaded B2B provides the Customer Group (i.e. be able to secure categories and/or products by group and tie the user to a group to restrict access) functionality, are there any other options out there?