There are many libraries featuring impulse responses online, both free as the great EchoThief and commercial, such as those impressive recordings Audio Ease has been doing for the Altiverb reverb plugin. But there is something actually beyond all these options, at least in terms of research and sonic exploration. It’s called OpenAIR (Open Acoustic Impulse Response), a collective IR library that aims “to provide a centralized, feature rich and future proof on-line resource for anyone interested in auralization and acoustical impulse response data”.
Supported by Art & Humanities Research Council and run at Audiolab in University of York, OpenAIR features mostly creative commons licensed recordings of impulse responses by contributors from all over the world, allowing not only to download files, but also to listening to demonstrations and learning about the details behind the recordings, places and buildings captured, including a lot of interesting captures of the reverberation and sonic qualities find in architecture and environments.
You can visit their website for download, and there’s also a way of registering as contributor for sharing your own impulse responses.