After the iPhone app store through the iTunes, and Nokia too announcing their online store, now Blackberry is announcing that its going to open the App store for the blackberry mobile devices very soon, with everything that would be handled within its interface and apps would be sold without any 3rd media sources.

Accd. to the Blackberry site -

Coming soon! Find tons of great applications designed for your BlackBerry® smartphone in one convenient place – BlackBerry App World™. Personalize your BlackBerry smartphone with games, social networks, personal productivity applications and so much more. Message your best friend, track the stock market, or channel your inner rock god. Sign up to receive updates for BlackBerry App World today and discover how to put more of your life on your BlackBerry smartphone.

No one is sure what Blackberry would do with the previously popular and linked stores like Handango etc. which were dealing with the Blackberry apps earlier, and Blackberry used to refer people to those stores if any apps were searched for.
Check this page to see about the developing store, or get subscribed to the updates about the store.

You can still purchase apps directly from the store right now, which are through various sources and you need a paypal account for that.