As you guessed - you have couple of options -
You can just go with Alfresco, which has Alfresco Share also working on top of it. Alfresco Share has lot of features which might match your requirements. Share provides a team collaboration environment (Wiki, Blog, Discussion, Document Library and Dashboard) with dashboard features which also includes customizable and configurable dashlets (like portlets in Portal). However, you will have to define your requirements further more to see if Share will exactly match your requirements.
If you ask me - you can definitely achieve or extend Share to match whatever you could do in a Portal (any portal for that matter).
Other alternative is Alfresco and Liferay (or JBoss) Portal. Hope this helps!