Microsoft made available the Bing Map App SDK to start building, testing and submitting applications to Bing Maps to be featured in the gallery. Download SDK which comes with Bing Map App template and start cranking away on your project in Visual Studio (note: the Bing Maps site was upgraded to Silverlight 4 - read more about the changes to Bing Maps). Once you've created your app, you can test it on the site itself. That's right! The developer sandbox is the actual site. You simply need to go here, click the map apps button and you'll unlock our secret Bing Map App Test Tool.
"Tool is what you need to test your apps prior to submission to Bing Maps for display and use in Map Apps Gallery. To use the Tool you'll need to append "?Developer=1" to Bing Maps URL which'll load a specific catalog of Bing Map Apps. Click Map Apps button and select tool. To test your app, you'll need to load all your plug-in by clicking "Choose Plug-in Assemblies" button. Then, click "Add Supporting Assemblies" button to and load your supporting assemblies. When complete, select Next and Bing Maps will verify build. Provide a name, description and set of optional parameters describing your map app. To submit your app, login into Bing Maps Portal. Click "Submit a map app" link. Complete form with map app name, description, publisher, select custom map app, choose an icon for your map app and attached your assemblies all zipped up. Agree to Bing map app submission addendum, then click submit. Your app will be reviewed, so check status on the portal until it's published."
Download: Bing Map App SDK