I've been diving into the deep end of integration type stuff lately. I've done work in that arena before, but recently committed to learning craploads more about this stuff so, being myself (cheap, novelty junkie, open source whore) I've been poking sharp sticks into the open source stuff around (as well as the really expensive stuff -- some of which is pretty impressive).
Current playthings include:
Additionally, I fully agree with Steve Loughran's assertions in his Alpine paper. You are working with XML -- accept that. One of the things I really like about XFire is that I can use XMLBeans -- the most "true" Java-XML mapper I know of -- XOM would be nice as well. Something xpath-able at a minimum.