Josep just sent me a link to the launch of the MetrO for BlackBerry beta. The application lets you get public transit information for over 400 cities stored on your BlackBerry. Sadly it does not have the transit maps but it gives you very detailed and customizable directions on how to take public transportation. I think the coolest part is that the directions are stored on the device so no excessive bandwidth. Hopefully it will let you store them on an SD card soon.
You can get a basic idea of the application in the images below:
I am currently loving this on my BlackBerry. I take the subway every day so this is very useful when I need to go somewhere new. The best part is that since it does not require a data connection after the initial install it will work in the subway.