- The documentation of the Tkx distro itself; it includes a Tkx::Tutorial.
- The perl.tcltk newsgroup. It is archived here.
- TkDocs. Has reference materials and tutorials. Perl examples are for Tkx, not Tk!
- Tcl/Tk documentation - the horse's mouth.
- Online documentation for ActiveState Tcl.
Also check out Tcl::pTk, which provides direct access to Tcl/Tk (that's right - Tcl) but via the Perl/Tk.pm syntax you know and love.