Can someone recommend a good diagram tool?

I need to make a presentation middle next week on how to scale a massive system and need to draw some diagrams. Diagrams will contain about 150+ systems / blocks with many lines all over the place and I need to be able to animate lines connecting and disconnecting between them.

Powerpoint's diagramming tool is quite poor compared to something like Gliffy which I've used before. I don't remember Gliffy having the capability to make diagram animations though.

Any suggestions ?