Serious Sounds has a free sample pack available for download, Hard & Bouncy Volume One.
The Audio Pack contains over 500 high quality royalty free audio samples (wav format) in a simple and clearly arranged structure over 21 folders (excluding sub-folders).
Hard & Bouncy Volume One is aimed at music producers producing any genre Hard and or Bouncy such as Nu NRG, Makina, Bounce, Hard NRG, Hardcore, Hard House, Scouse, Hard Trance, Happycore or Hardstyle (although they are probably suitable for any electronic genre really).
Hard & Bouncy Volume One is a free download. A package with artwork is available as well.