Tools to measure in room response

K, you have received good advice so far.
I would like to add that the most musical in-room response is not a straight line in the treble range. Most listeners perceive a flat treble in-room response as bright-sounding.
A gradual roll-off starting around 12 KHz is correct for off-axis, far field listening in a room with standard furniture / carpets / curtains.
By off-axis I mean slight toe-in, as recommended by most manufacturers.
Adjust speaker tilt and toe-in to achieve a gradual slope, with no major peaks or valleys.
I hope this helps

I use a portable phonic PPA3 RTA and achieve consistently good results.

Its built-in microphone is calibrated, you can store the data in your computer through an USB port and calculate the average of several room response graphs (just like John Atkinson does in Stereophile room response meausurements).
It comes with 31 band spectrum analyser, SPL reading, EQ setting calculations/suggestions, RT-60 calculator, phase checker, a built-in test tone generator and a test CD.
Last time I saw it cost U$ 500, a great investment if you really want your system to shine.

The learning curve is quick, in 30 minutes you are set to go.
In most systems I can find a much better loudspeaker positioning after 3-4 readings.
Usual disclaimer...

Glai:
Thanks for the info. I will look up Fuzzmeasure.