Here is a script to display each widget available in Tk. It made the assumption that all widgets begin with a lowercase letter.
#
# the dynamic list of Tk widgets
#
package require Tk;
set tkCommands [lsort [info commands "::tk::\[a-z\]*"]]
foreach cmd $tkCommands {
puts " [string range $cmd 6 end]"
}
exitIt gives :
button canvas checkbutton entry frame label labelframe listbox mc mcmax mcmaxamp menubutton message panedwindow radiobutton scale scrollbar spinbox text toplevel