I think urxvt has this feature, but it's also available via the Universal Input Method System in many widget sets and it is supported by both Gtk and Qt (might need some additional packages to be installed/setup). So I can just type the symbol in hexadecimal with Ctrl+Shift+U 2 6 0 3 Enter to enter .
I used to remember the unicode symbol for long dash—but now that I use EUR keymap I don't need to, and I've forgotten it :).
edit: oh crud, HN filters snowmans :(.