Line56 has some suggestions:
A good place to start your portal implementation is within your divisions. Seek out areas within your company where daily collaboration between divisions or external audiences (channel partners, vendors, even customers) is required. Portals can help lower the friction in the exchange of information between these groups, which leads to lowered administrative costs. Some suggestions for small-scale portal projects include:
Improving the way your sales, purchasing and legal departments store, manage and distribute contracts
Creating a single repository for all of your marketing materials and extending access to your channel partners
Pulling all of your call center applications into a portal “composite” application and improving the efficiency of your customer service representatives.
Linking all your internal websites into a single “super” portal with search capabilities