One of the more sophisticated animation tools out there is Blender, a cross-platform, free suite of 3D creation tools. Blender allows a lot of animation tricks that are normally only found in packages costing hundreds or thousands of dollars.
The eclectic, artistic, and highly-animated Jacek Antonelli has released a script, scene and animation skeleton that allows users to create and export high-quality animations from Blender into the BVH format used by Second Life.
'The biggest advantage of Blender (over, say, Qavimator),' says Antonelli, 'is that I can tweak the animation curves, and make them nice and smooth.'
'Blender also has a powerful system for creating rigs, different ways of setting up the skeleton to make certain types of motion easier. For example, the rig in the blend file can rotate its hips without moving the whole body.'
Antonelli isn't providing technical support for this release, but is just making her own tools available under the Creative Commons Attribution 3.0 United States License.
If you're already familiar with Blender, or you want to get into more advanced animation tools for Second Life animations, you should give this a whirl.
(A new version of Blender was just released, so they're experiencing crippling traffic loads at their website right now)
