Free sound libraries
All officical Hydrogen drumkits are hosted on SourceForge.
These libraries can also be downloaded and installed from within Hydrogen. Goto Instruments > Import Library. Hit Update list', select the library you want to install and click the Download and install' button.
More free and non free drumkit links
These Drumkits are not tested by us or have licences that prohibit us from distributing them. You can use all of them for free.