For a while I've been a faithful user of Lyx for my mathematical word processing needs. But recently I have been seduced by TeXmacs. This is a beautiful program. It's like an antique, in the best sense of the word - a real polished work of art. It's VERY Unixish, so much so that it practically has a beard. You have to download Cygwin to run it - though they bundle a version if you're lazy. It has a very well-designed set of keyboard shortcuts: if you are typing Maths and want to use a Greek letter, you just hit the Latin letter, then tab. Hitting tab again gets you variants. If you want to type a greater than or equals sign, it's just > then = and it will automatically compose them together for you. Similarly, the empty set sign is just @, / and tab.
OK, enough said - if you're the target market, check it out.