I am using a lot of XSLT in my work with Sitecore 4 and 5. Practically every component that reads from Sitecore I do in XSLT. Only backend, formulars and business logic is programmed in c#.
One of my colleagues reminded me about this XSLT Quick Reference from Mulberry Technologies. A very nice 2-page quick reference that can be printed and hung on the wall. And guess what: They have one for XSLT 2.0 also.
XSLT and XPATH 1.0 Quick Reference: http://www.mulberrytech.com/quickref/XSLT_1quickref-v2.pdf
XSLT 2.0 Quick Reference: http://www.mulberrytech.com/quickref/xslt2.pdf