Check out Xopher and Delano’s One Time Secret:

When you send people passwords and private links via email or chat, there are copies of that information stored in many places. If you use a one-time link instead, the information persists for a single viewing which means it can’t be read by someone else later. This allows you to send sensitive information in a safe way knowing it’s seen by one person only. Think of it like a self-destructing message.

I love the attention to details like only being available under SSL. Pretty simple, useful and clever tool.