All, I searched for 5 pages to find the cool application threads, but to no avail.
With that said, if anyone searches for XSLT, this should come up.
TestXSLT is an excellent Mac Application. It's a little older, so I'm guessing it's not universal(though it says it is -- could just be written in java and that is the where the slowness is from), but it has made my life a million times easier when working with XSLT.
It can be downloaded
here. I think you'll really love it as its very intuitive to use.