For mathematical writing I've been using Lyx which is a Latex WYSIWYG application. Once you know the shortcut keys it works rather well. Nowadays I often work directly in Lyx rather than on paper first and then type it into Lyx. It encourages you to work cleanly and correctly rather than quickly and sloppily, so in the end it saves me a lot of time. The big disadvantage is that it's hard to incorporate drawings.