Character Maps for Linux

Ever had to make use of special characters? For example, to put an equation like ∫x² dx in an OpenOffice document? How do you get at those characters, anyway?

In Windows, there's the Character Map, via Start Menu -> Accessories -> System Tools -> Character Map. For KDE users, check out kcharselect. Gnome users should look at gucharmap. I've not had experience with gucharmap, but kcharselect has a very good search feature, "categories", and a description of the selected character.