Despite it's beta status, ardour is in extra now. Some people who tested it encountered some rough edges, but as one of the best developed audio applications around it is in the official repos. It's not really self explanatory so reading the documentation pdf on www.ardour.org is mandatory. It is recommended to run jack and ardour as root to get realtime capability. This causes some serious security problems on your system. Make sure you know what your doing and better get disconnected from the net with that box during your ardour session.
Also monodevelop has made it to extra now. As a dependency of gecko-sharp it requires mozilla-firefox. With Arjan and Jan's efforts to find a better place for mozilla and friends, monodevelop will have to be restructured a bit but currently it works as is fine.
Last but not least, the xsp server is in extra now. XSP is a mono-based HTTP server that can serve ASP.NET. Currently only xsp is in the repos and that is not for production. mod_mono, the connector between XSP and Apache, which will give you a production quality application server for ASP, is still under testing but will be made available soon. Read the post_install message to get started.