As I open up this section, June 04, with the W3C WD only just beginning to stablize, I can count 1.5.
Saxon has been there for about 8 iterations, and is now available with Schema support in paid mode. Another is announced.... but so far, that's it.
Saxon Saxonica is the home page, with links to two versions: the basic edition Saxon-B, available as an open source product from SourceForge, and the schema-aware edition Saxon-SA available on a commercial license.
Ednote: June 2004
While not yet as "reasonably complete" as Saxon 7.9.1, the Oracle10g XML Developer's Kit that you can download from Oracle contains our in-progress implementation of XSLT 2.0 in it.
In case you were looking to work with multiple Java, XSLT 2.0 engines.
For example, I believe we've implemented the new grouping features, but not yet the ability to define functions in XSLT. I
If you need virtually all XSLT 2.0 features, then Saxon is your best (only? Java) bet for now.
Just wanted to send up a flare that other major vendors are working on XSLT 2.0 implementations, too. Michael Kay's just a little more nimble with Saxon than we've been able to be so far! :-)
As we've done with XSLT 1.0, we'll ultimately offer both Java and C/C++ implementations of XSLT 2.0 as part of a future maintenance release of the Oracle XDK. Our inside-the-database XML DB functionality depends on the C implementation, for example, for XML parsing and XSLT transformation (among other things).