We're not sure how useful this is to most Fabbaloo readers, but it is very cool. The Materials Project is an online database of, well, materials. Once you register for free you can access the service by entering a chemical formula and the service returns you a wealth of information about the selected material. You can also search for partial formulas or specific properties. They also include a Reaction Calculator, Phase Diagrammer, Li-Ion Batter Explorer and a Structure Predictor. Not being chemists, we don't know what those mean, either!
The project is a collaboration between MIT and the Lawrence Berkeley National Laboratory and appears to be slightly experimental at this stage, at least when you look at the signup disclaimer:
I understand that the data in this database is computed, and may not be accurate enough for my application. I agree not to hold the developers, contributors, and hosts of the Materials Project liable for any accuracies in the data, or consequences thereof. I agree not to use automated scripts to collect large fractions of the database and disseminate them. If you are interested in large datasets, please contact the developers.