Go Design Something: Building Your Job-Winning Portfolio
Kristin Anthony's free course on building an instructional design portfolio
Volunteer Opportunity to Build Your eLearning Portfolio | onehundredfortywords
Info on an organization looking for volunteer instructional designers/developers to create content for job seekers. They are OK with content being used in a portfolio, so this is a good place to gain some experience and get something to show for a portfolio.
Here’s Why You Need an E-Learning Portfolio - The Rapid eLearning Blog
Benefits of a portfolio plus tips on what to include and what to do if everything you do is proprietary