While the Apple Watch won't be released until April 24th, users can try on the watch in Apple Stores beginning on April 10th. Presumably you'll be able to test the watch with some of these applications.
Here's a few that have been updated with Apple Watch support already:
● Dark Watch
● MLB.com At Bat
● SPG: Starwood Hotels & Resorts
We'll let you know as more get approved. Please follow iClarified on Twitter, Facebook, Google+, or RSS for updates.