The Bamboo Project Blog: Using Del.icio.us to Create an Easy, Always Updated Online Portfolio
If you are already posting your work online, use a social bookmarking tool like del.icio.us to collect everything in one place. As you create more work, just bookmark it and tag it to update your portfolio.
How To Create ePortfolios with GoogleApps (eportfolios)
Helen Barrett calls Google Apps the "best free Web 2.0 tool for maintaining an online personal learning environment" that can be used for eportfolios and assessment.