There's a terrific post at Bankrate.com on a subject most folks don't think about when creating their estate plan — who will know what your passwords are so they can access your accounts? There is now a service called Legacy Locker which will store them on-line for $30 per year. Whether that service is right for you may depend on how squeamish you feel storing your passwords somewhere out in the cosmos.
Of course, you could do things the old-fashioned way — write down a list of all your passwords, along with a list of your accounts, life insurance policies, safe deposit boxes, etc., etc., and give them to your attorney or someone else you absolutely trust to safely store the information. If you do that, you and your lawyer should have an agreement describing the circumstances upon which that list will be released and the person(s) that it may be released to.