“Headache with Pictures” is a small, but usefull plugin for your dashboard: It offers an area to quickly write down things you’ve got on your mind. This can be things to blog about or your shopping list. (The title is an allusion to Futurama.)
If you blog with multiple persons, you can leave a message for the others. In the plugin file, you can determine, what capabilities a user must have to read the notes, and what capabilities he must have to write/modify them. By default, Authors and higher can write, and every registered user can read.