I'll try something wearing the council hat. Thanks for raising this issue.
Right now the best place to find applications from stable Nokia (OVI store) and community (maemo.org) repositories is from Maemo Select. You can browse to the page with your N900 and simply click on the "download" link for an app or widget that you want. An install script should then open the Application Manager on your device, add the stable repository from downloads.maemo.nokia.com or repository.maemo.org/extras/ to the list of application catalogs monitored by your device, and begin installation and you will be good to go.