MathType 7.0
MathType is a powerful interactive equation editor for Windows and Macintosh that lets you create mathematical notation for word processing, web pages, desktop publishing, presentations, elearning, and for TeX, LaTeX, and MathML documents.
Works with 700+ Applications & Websites:
A few of the most popular:

Microsoft Office

Apple iWork '09

Adobe InDesign

iBooks Author

WordPress

Maple

GMail

Blackboard

Evernote

Moodle
More Ways to Create Equations:

Entering Math by Hand: Enter equations as easily as you would write math with paper and pencil! This feature uses the builtin handwriting recognition in Windows 7 and later.

PointandClick Editing with Automatic Formatting: Create equations quickly by choosing templates from MathType's palettes and typing into their empty slots. MathType applies mathematical spacing rules automatically as you type.

Keyboard Shortcuts: Save time using keyboard shortcuts. MathType has customizable keyboard shortcuts for virtually every symbol, template, and command.

Type TeX or LaTeX: If you already know the TeX typesetting language, you can enter equations directly into MathType or Microsoft Word documents. TeX editing can be mixed with pointandclick editing so you get the best of both worlds. You can even paste in equations from existing TeX documents.

CopyandPaste: If you created your equation in another application or found one on a website, why take the time to create it by hand again? Simply copyandpaste it directly into MathType, and it is ready to edit or use in your work.

Save Expressions in the Toolbar: Drag frequently used equations and expressions to the MathType toolbar so they can be inserted later with just a click or a keystroke.

Find Symbols: MathType's Insert Symbol dialog allows you to explore the available symbols and insert them with a click or keystroke.