I'm testing out the sensors one-by-one for the first week (just to make sure they all work and can transmit/receive data when connected to the Arduino). The Arduino is connected to the computer by a USB cable. It's also where it draws the power (5V max).
(Please excuse my terrible picture quality. Image on the left is created using Fritzing.)
The photocell is ordered from here: http://www.sparkfun.com/products/9088. Plugging the data input into the analog pin and running some code will theoretically display a value between 0 and 1023 on the computer screen. This represents voltage measured on a scale of 0V to 5V. In reality, however, if I cover the photocell, the value will drop to ~100, and if I shine a bright light on it, the value will jump to around 1000. Room value is around 870.
Current Usage: 250 mA with the 10K resistor.
The Temperature/Humidity Sensor is ordered from: http://www.sparkfun.com/products/10167. Its calibration is a bit complicated, so we used code from here to test the sensor.
Room Temperature: 24 degrees C.
Room Relative Humidity: 53%.
Current usage: 20 mA.
We also ordered a humidity only sensor (http://www.sparkfun.com/products/9569). However, since humidity depends on temperature, we ended up just connecting both the humidity sensor and the temperature/humidity sensor onto the Arduino. The reading for humidity seemed to agree, which is good. It seems that it's just more efficient to use the temperature/humidity sensor, as this one doesn't seem to give us any additional information.
The current usage seems negligible. It registered as 0 on the multimeter.