The list is a bit old, but maybe it helps with some odd keys. Now that unicode is pretty common, I try to stick to the ellipsis for example… I have to say that the compose position for dieresis is a bit more logical (compose-" as opposed to macs alt-u), which is quite useful if I don't want to switch keyboard layouts when typing a bit of German (or write a lot about Motörhead and Queensrÿche).

X11 also has "level 3" support, which is straight-forward additional characters when pressing a certain key, as opposed to combining multiple key presses. Mac's alt key basically does both to a certain degree. The fact that it's turned on by default and the keyboard viewer makes it a lot more common usage in my experience.

1. Change your layout from "USA" to "USA International (AltGr dead keys)". Then use right-alt+key to make various special characters (you can look at what each character does at "Show Current Layout").

2. Enable the "compose key" -- I use the Menu key for this -- which is described at http://sivers.org/compose-key (it's simple to enable: Keyboard Preferences→Layouts→Options→Compose Key Position). Both of these are customizable, so you can add your own combinations if you want.

There are some other ways:

3. Ctrl-Shift-U in a GTK+ text input to enter a code point, as you said.

4. Alternative input methods that let you type special characters in in various other ways, such as LaTeX names, if you prefer that.

Yes, please! This would be extraordinary! How do I do it?

←/→ move left or right one character.

⌥ + ←/→ move left or right one word.

⌘ + ←/→ move to start or end of line

To swap the command and option keys, but just in the terminal, you can use: http://github.com/aim-stuff/cmd-key-happy