Want to test my monitors for flatness, but what am I missing?
 

I found this freeware frequency and spectrum analyzer:

http://www.sarand.com/prd/winsingad/winsingad.html

I've got a pretty flat mic. But what do I play through the
monitors? Do I need some type of tone generator to
step through the frequencies and see how it looks
on the analyzer?

You need a pink noise generator and a Real Time Analizer if I'm understanding your question right. Adobe Audition has a noise generator built in. I belive most other audio editing programs will also, but I'm just assuming there.

Dave,
You can get a 30-day trial of a much more sophisticated ($600) system, that includes everything you need (including online tutorials here:
http://www.ymec.com/products/dssf3e/
I've used it to analyze the inputs of my cams and the DXA-8

They also offer a $24 subset (their Real Time Analyzer) that includes a tone generator with a sweep function, an oscilloscope and several other functions.

What really is pink noise? Just by playing this
pink noise, the analyzer can tell how flat my
monitors are, assuming my mic is flat?

Pink noise are tones that contian the freq's that are reproduced at the same level to test your monitors. OK here's the deal. What has been suggested above will only test your outputs. Not the monitors. You need a RTA that is set in front of your monitors in the place that you listen to them. Placement has an effect on what you hear a when you hear it. IE... a 20KHz wave moves much faster over a distance than will a 80Hz. And because of this looses energy faster and can't be heard at greater distances unless pushed harder.That that's the reason that made the BBE processors and time correctors. So directly in front of your monitor you may be hearing a flat response, but because of the placement and distance what is getting to your ears is not. Although in a small setting like a studio this is not as noticable than say a concert.

Hopefully that freeware program I found has the
pink noise in it.
So, the pink noise runs through all the different
frequencies? Like, steps up from low tones to
the high pitched tones?

Pink noise contains all the tones at once.

You can also try a test sound which uses sine wave tones which change from low to high. I believe this will give you a different result than pink noise.