I've spent a large chunk of the last weekend playing with the Silverlight PivotViewer from Microsoft.
Despite the official upper limit on number of items being "3000", I've taken it up as high as 73000 items now - the animations don't work at that level, but the pivotviewer is very very useful there!
You can see some screenshots (attached hopefully!) and there's also one "live" demo on http://zoom.runsaturday.com
The only downside - there have been a few issues I've had - one of the key ones of which is:
- if you create a .cxml collection in which items don't each have unique images (e.g. they share a default image) then the Silverlight control does something odd - it somehow seems to try to duplicate the shared images and uses up lots of CPU and memory as a result.
This bug is reported in a bit more detail on this thread - http://forums.silverlight.net/forums/t/210211.aspx: