This website provides a collection of surveys used for a variety of purposes. There are a variety of Electronic Portfolio research projects identified on Dr. Barrett's website.
The pages on this site (linked on the left) highlight some of the instruments used in a variety of studies. In addition, the ePortfolio Surveys page has links to a few other surveys developed for published research studies.
I also recommend getting the new book, Electronic Portfolios 2.0, the report of the first three cohorts of the National Coalition of Electronic Portfolio Research.