While Duct Tape may hold the world together, Gaffer Tape can mend anything except a broken heart or a bad haircut, so they say.
'Gaffer', 'Gaff' or 'Gaffa' Tape, likely named after the movie term 'gaffer' for the techie gang, is vinyl- or polyethylene-coated cotton cloth tape used and loved by stagehands all over the world for its high usability and performance. In colors or white, it's for marking and labelling things (like the lights and sound setup on a mixer console). In black, it's for everything else.
Proper gaffer is not your cheapass homeland security duct tape. You can easily tear it to arbitrary rectangles of a few millimeters size - with the tips of your fingers. It's curl resistant, you can write on it and it's not glossy but matte, so it hides well on a movie set or stage. It sticks, holds and seals incredibly well, yet removes cleanly.
The popular choices for good gaffer seem to be "Permacel 665" and "Nashua 357". (Use this info with caution, I rarely have the chance to use proper gaffer and cannot memorize the name, so these are from the web. 'Permacel' seems to ring a bell though. /msg me if you know any good gaffa brand. Also, I couldn't find any factual info on a supposed 'gaffa' trademark).