There is an interesting talk on Papervision at the Blender conference:
Finally there is a way to get 3D into Flash, from Blender (or another program such as 3DsMax), with Animation! It's a tool called Cast3D.
Check out this:
You can download the Papervision 3D component for Flash CS3 from here:
I thought this was a very cool demonstration of the fluid capabilities of Blender. It shows a "magician" character, who "magically" conjures the water into different shapes:
Some links to free 3D models, that are compatible (.blend file, or can be imported) with Blender:
I came accross this open source 2D annimation tool called Synfig. It's still in beta phase, but it looks to be pretty interesting. One of the things it's supposed to be really good at is tweening. It's intended more for Film and TV type annimations, rather than typical net stuff. I'm not sure if it's going to be as good as After Effects or Flash for most things, but it could prove useful for something!