The Pebble e-paper watch is a very cool accessory for your Smartphone that is currently having a kickstarter campaign, and these people have already made a product for Blackberries.
The only downside it is uses the old Bluetooth 2.1 tech instead of the new lowpowered bluetooth that the iPhone 4S has, so it will drain battery life.
Still a very cool idea, and a product that will have a future.