I'm looking  for cheap sensors, specially for chemical.

I've found this sensor portal page, and has usefull information about sensors. http://www.sensorsportal.com/HTML/Sensor.htm

Temperature sensor KTY81/210/B

I am continuing to read Tiago thesis, nice ideia for providing usefull content with low cost available technology and free :D

Today i met with Felipe Santos, and he showed me some available sensors as well told me what they have there. - humidity - temperature - monoxide carbon - light - infrared - distance

He told that some sensors were purchased in"figaro sensors", in the lab they have a nice custom base for sensors built by them. This base has an wireless module transmitter (xbee),  and with their base they can get signal from many sensors by wireless.