With Agender you can associate notes with some date or with no date in particular, you simply start it and it will create a task-bar icon and stay in the background, without annoying you, it can run on login. Visit the website to see more.
Agender in Windows Se7en
Agender main window
Agender runing in Fluxbox 1.0.0
Agender showing year selector
one of the more strange features of Agender (only on GTK)