I've collected a bunch of extra DEFLATE targets that W3TC doesn't seem to be using - they may be unique to some apache installations, but might as well make W3TC handle more cases, right?
I would also like to throw in
application/json, which surfaces when you install http://wordpress.org/extend/plugins/json-api.
And finally, just to make sure the most important things work on setups I'm not sure about, I usually add this:
# DEFLATE by extension AddOutputFilter DEFLATE js css htm html xml
Feel free to use these in the plugin, Frederick.