I've recently been given a Raspberry Pi and have been trying to come up with a good idea about what to do with it. I eventually decided on a Raspberry Pi powered weather station.
The idea is use the experience building the weather station to expand my knowledge in programming, electronics, meteorology, and data collection.
So far all I have is a small temperature sensor set up that takes a reading every 5 minutes. I'm looking to soon add an anemometer (wind speed sensor), and precipitation sensor. The readings from the Raspberry Pi are uploaded to my database where I use R Shiny to pull the data and present it on a webpage. With more data shiny makes it super easy to come up with interesting statistics and graphs.
Shiny app: http://cluoma.shinyapps.io/ShinyTest
Raspberry Pi Code: http://notez.ca/downloads/temperature.zip
(I've since stopped paying for my own server so both links will no longer work. If you interested in the code for either please email me)