I use "LaTeX Equation Editor" together with "TeX FoG". If you want nice looking equations this is the best way to go. Alternately, you can use the mostly crappy Microsoft Equation editor, but it makes your math look like poo.
There are a number of editors that allow you to enter LaTeX equations and output pdfs, and I like them pretty well.
There's also this website: http://www.sitmo.com/latex/ that will output a .png file. So, scaling it up looks poor, but it might work for what you need.
If you have teTeX installed--either the MacTeX or another installation--then you can use LaTeXiT. There are other suggestions on this forum. You can find them by searching on equation editor.
They both work well with many word processors (including Pages) and support the automatic baseline alignment when inserted in a text line.
You can drog&drop or paste MathML, Wiki equation, LaTeX, or MathType equation into MathMagic window to re-edit it.
MathType supports copying out equation as LaTeX or MathML but pasting is not supported.
Free "Equation Editor" was bundled with some word processors in the past. You may find a Universal Binary version of Equation Editor in AppleWorks 6.0.
These are all GUI based equation editors for easier and faster input.
MathMagic seems to offer much better equation quality.
If you need the computation capability and graphing, MathEQ or LiveMath can be an inexpensive solution. www.matheq.com