At this year's TechEd, Andrew Bryan of Dundas Software presented a session on Custom Report Items (a new feature of SQL Server 2005 Reporting Services). Several people have asked me to post the code that was shown in the session so I have done so here.
The code should compile with SQL Server 2005 June CTP and Visual Studio 2005 Beta 2. There is a bug in the Report Designer in the June CTP in that the design-time control properties do not show up in the VS Property Window. You will need to add your own dialog if you want to set properties. This will be fixed in the final build.
As we were not able to fit documentation on Custom Report Items into the SQL Server 2005 Books Online, we plan to provide a white paper and fully documented sample later this year and will eventually get it into a refresh of the the standard docs. For now, you are going to have to play with the code to get it working.
BTW, Dundas is providing an upgade to the Reporting Services chart component. I encourage you to sign up for the beta.