I'm surprised no one mentioned Lyx yet (http://www.lyx.org/) This is a WYSIWYM processor (What You See Is What You Mean) :)
It lets you write text and formulas in a close to wisiwig thing but its all latex inside.
I've found that just writing LaTeX source is much easier than tracking down the appropriate menu item/dialog box in Lyx. Plus, LaTeX is more commonly installed than Lyx, so I'm more likely to be able to work on school computers, and if it comes down to it I can edit my LaTeX source in any old editor, then test it at home.
