I've been studying algorithms about collective intelligence, for things such as recommendation engines, neural networks etc., and was looking for freely available datasets and/or APIs for practice projects. any suggestions?
Here are some examples of the types of things I was looking for:
Delicious API: collection of links, tags, who liked them, etc.
Ebay API: resource of various items, prices, descriptions.
Maybe the UCI Machine Learning Repository is what you're looking for.
http://archive.ics.uci.edu/ml/
Weka's website (a collection of Machine Learning algorithm) also features a list of datasets: