Re: XML / XSL Editors

XMLSpy is probably the most known of the editors, i think i'll begin
with it.

I second David's suggestion that you try oXygen.  There's a free 30 day
demo, and it's a really nicely done editor and xslt tool.  It's also
much cheaper than XMLSpy, and likely more compliant.

Consider, for example, a recent schema I was dealing with that was
authored in XML Spy.  It had more than one show-stopping errors because
XMLSpy didn't catch them, and the author hadn't bothered to cross-check
with xerces or another schema validator.  My understanding is that this
is not an isolated example.