If you haven't seen Itead Studios Nextion displays and you want a display for your next Arduino project take a look! If you've ever used .Net forms then you'll feel right at home. It's not perfect and you're not going to make smooth animated objects due to the lack of double buffering but it's far better then a text or graphics LCD.
Use the Nextion Editor to design and compile your "forms" with any components (text boxes, picture boxes, gauges, sliders....) and place the compiled image onto an sdcard. Throw the sdcard into the display and it will flash the firmware after which the microsd card is no longer required. The components on my display are only pictures and text boxes. Itead's built in gauges are very limited but if you can draw it in Photoshop (I made my graphics in PowerPoint!) you can display in on the Nextion.
DHT22 Temperature Sensor
£3,50 from ebay and gives the temperature and humidity to 0.1. There's a great library called PietteTech_DHT for the Photon which makes reading the DHT22 almost too easy. The only issue I found was that I was using an interrupt for the light sensor which was interrupting (pun intended) the precise timings needed to communicate with the sensor over a single wire. Simply remove any other interrupts before reading from the sensor and reattach them once complete. The PietteTech_DHT library also uses interrupts so disabling them isn't an option. I'm polling it every 5 minutes so missing a flash of the meter every 5 minutes isn't an issue as the previously recorded value will be resent if needed.
TSL257 Light to Voltage Sensor
It's simple, cheap, and VERY sensitive. I've duck taped it to my electricity which is made of perspex. Opening the door to view the meter is enough for the sensor to read high! Lucky really as the LED is so dim it's sometime hard to see the flash but the TSL257 catches it every time.
The only piece of software in this project is emoncms which is part of the OpenEnergyMonitor platform. This has a fantastic API which makes it easy to push and pull data from the platform. As well as a good webpage where you can manage and view your data in a number of dashboard and graphs. The two Photons use http get request to push the current watt hours, temperature, and humidity as well as pull the current and historic data via the api. This can be hosted yourself on a linux or windows server or you can use the public version at emoncms.org. I work for a Cloud hosting company so hosting a linux server wasn't an issue. Currently the Cloud version has not been upgraded since 8.35 where as self hosted has seen versions 8.5 and currently 9.0 RC.