Technically, you can only display in your portfolio these sites IF the agreement with the client gave you the permission to do so; otherwise, since they would have been made as "work for hire," which means that they belong 100% to the client, you would not have a right to make use of them for your own purposes. This would not be a "fair use" permitted under the law. Going forward, the developer should make this part of his or her agreement with clients; that he or she can show samples (the amount of which can be defined in the agreement) as part of his or her portfolio.Note that the designer has an easy way around this: don't actually incorporate the work into the portfolio, but give a prospective client the web address and tell the client to take a look. The website is available to anyone who logs onto the right address (even on sites with subscriptions, the general public can always get to a page or two). Someone can always say, "Take a look at X; I made that."