The Reference card (52 half-pages, for Tcl/Tk 8.0) can be found at http://tiger.la.asu.edu/Quick_Ref/TclTk_quickref.pdf
22 February 2008 : Dead Link, but if you google for TclTk_quickref.pdf, you find a variety of copies, like http://scout.csu.ru/ftp/Manuals/TclTk_quickref.pdf . 24 January 2009. Dead Link, try here: http://dreamsworld.dr.funpc.de/quick/TclTk_quickref.pdf or here: http://library.baldwinsung.com/Programming/TclTk_quickref.pdf
An attractive on-line alternative is Brian O'Hagan's Command Reference Guide [L1 ].
However, it would really be useful for someone to get the source text of one of these into a currently used format and add them to the Tcl and Tk source distribution...