If you look to Salesforce as an instrumental part of your business success, it's often worth taking a look at the benefits of Professional Edition. In addition to administrative features such as the sharing model which supports larger groups, Professional Edition includes;

• Leads, Web-to-Leads, Mass Email
• Sales Methodologies, Sales Forecasting, Contracts
• Agent Console, Solutions, Suggested Solutions
• Self-Service Portal, Web-to-Case
• Custom Tabs and Custom Tabs Objects
• Dashboards

You can also purchase offline, wireless, campaigns, and price books as add-on modules with Professional Edition. If you are interested in making more out of AppExchange, that may be yet another reason to upgrade. With Professional Edition you can grow into more custom tabs, custom apps, and a great selection of AppExchange Partners