Some web accounts are meant to be shared, whether with co-workers, clients you're providing access to, or for tech support. Passpack, the previously mentioned, online/offline password manager, offers a more secure way than emails or Post-It Notes.
You'll need to "invite" people from within Passpack, basically signing them up for service as well. Once you do, however, sharing a login and password to a site, without sending your data over email and leaving it up to someone else's security methods, involves just a few clicks. You set whether you cousin Joe just has access to the password, or whether they can modify it as well. By centralising a password with Passpack, you can also "push" password/login changes out to everyone logging in using their shared Passpack access, and can revoke access to certain folks or groups all at once.
Here's a video showing how sharing works in practice:
Passpack is a free service, with upgrades uncapping the number of (full-access) shared users, saved passwords, and other features. Intrigued but wondering about security and privacy? Here are their fairly full disclosures. Password Management & Provisioning [Passpack]