Open Data Sources
There a lot of free data sources with useful climate data to use on your next project. Here are few good ones to checkout.
OpenAQ - A really well done easy to use API of hourly air qualiaty data from around the world.
NREL APIs - A collection of APIs made available by the National Renewable Energy Lab. You will need to register in order to get an api key. You can find a variety of data here from utility energy rates to available electric vehicle charging stations.
NREL PV Rooftop DB - A database of suitable rooftop PV locations in the US
NREL Wind Integration Dataset - Historical timeseries US wind data
National Soil Moisture Network - Near real-time soild measurements from around the USA
Government Data Sites
These are not climate specific, but often government data websites have a wealth of interesting data to playaround with.