It's nice when people say nice things about you, though slightly embarrassing when they gush. Warm praise from Eliot Kimber at http://drmacros-xml-rants.blogspot.com/2006/02/some-tools-that-suck-significantly.html
Another tool that doesn't really suck at all is the Saxon XSLT engine from Mike Kay. Saxon is remarkable in being software of the highest engineering quality that supports essentially 100% of the relevant standards and is backed by exceptional support, especially given that it's just one man doing it and it's free, open-source software. I don't think it's overstating things to say that Mike Kay is a god among men and it's not within my power to meaningfully repay him for the value that Saxon has provided me personally. It's the only XSLT engine I use both for feature reasons (it's the only implementation that provides the collator extension support I need) and for quality reasons: it is as close to a bug-free piece of non-trivial software as I've ever worked with, and its fast. Wicked fast.