I am deaf and am constantly missing whispers (pst). It would be awesome if there was a mod that flashed the screen or a certain UI element whenever I received a pst.
Cellular. This goes a little beyond what you're asking (it creates a new frame specifically for whispers), but I love how it handles them in general, separate from the rest of chat.
Not exactly what you're looking for, but WIM has a blinking
image in the Broker/FuBar-Display when you get a message
and if your chat-window is open the register is blinking when
it is not the active register.
Some chat AddOns have the ability to flash a message on-screen (by hooking into the Raid Announce/Warning system or MSBT/SCT/Parrot's Notification area) whenever someone mentions your name. I am not sure if they have the ability to send all tells/whispers that you receive to this area, however that would not be hard to code in as a module).