I have recently installed a humidifier on my Bryant system and it works great. The unit is made by FIELD CONTROLS and is sold at home centers. It comes with everything you need to install it yourself, even a video.
This type of humidifier sprays a mist of water into your duct as opposed to relying on evaporation.
I had the evaporative type and it didn't do half the job of this one. It only costs about $100 and I installed it myself in about 90 minutes.
If you go to their web site you can order it online.