I did find one meta-post about sites that have Blackberry Applications, but many contained apps I would never use. So, I’ve created a list of the Blackberry apps I use the most (aside from the built-in apps):

• Twitterberry: I use this all the time. The new version supports alerts and scheduled updates as well.
• GMail: Another frequent-use application, excellent integration and presentation
• Google Mobile: Like GMail, this is an excellent port of Google tools such as Reader, News, Images, etc.
• BBNotePad: I have started using this more and more as a note-taking application.
• GridMagic: Great application for creating and viewing spreadsheets and sending them in XLS format via e-mail to your desk computer for further refinement.
• Viigo: Originally I didn’t use this very much, but after a while I found myself using it more and more. Even though it is ad-supported, I quite like it.
• Facebook: I wish this client was better for the Blackberry. Frankly, I don’t find it very useful as my Blackberry has no camera and the messaging is not as powerful as it could be.
• ReQall: An all-in-one application that does a decent job. I’m seeing potential in this.
• WPhone: This isn’t really an application for the Blackberry, it’s a plug-in for WordPress. It allows you to log into your admin panel and create posts, pages and manage your site from your Blackberry.

Hope that helps.