Text Document or Webpage
It is customary to put a works cited or bibliography at the end of a work. This is a fine location to put attributions when using textual work just like you would other citations.
If you are using an image within a document it is best to put the attribution information in the caption of the image.
Many videos and movies include a credits section at the end and this is the logical location for a list of attribution notices for other works used such as audio or video clips.
If the audio file is something that would aesthetically allow an audio statement of the attributions at the end (such as a podcast) then simply reading aloud the suggested information from the Text Document example for each work is suggested.
If the audio file would be harmed from such an addition (such as a normal-length song) then making sure to include the attribution information in any description of when you post the file online is recommended.
All Creative Commons licenses require attribtution (unless the contributor has waived that requirement), so no matter how or why you use a work, you must always be sure to note the author's name, the URL where you found the work, and the specific license that the work is licensed under. From the Creative Commons wiki, here are some best practices for attributing CC-licensed works:
If the work itself contains any copyright notices placed there by the copyright holder, you must leave those notices intact, or reproduce them in a way that is reasonable to the medium in which you are re-publishing the work.
Cite the author's name, screen name, user identification, etc. It is nice to link that name to the person's profile page, if such a page exists.
Cite the work's title or name, if such a thing exists. It is nice to link the name or title directly to the original work.
Cite the specific CC license the work is under, and link to the specific CC license, ie. for CC Attribution you would link to http://creativecommons.org/licenses/by/3.0. Note that embedded CC licenses often include this link.
If you are making a derivative work or adaptation, in addition to the above, you need to identify that your work is a derivative work i.e., “This is a Finnish translation of the [original work] by [author].” or “Screenplay based on [original work] by [author].”
It is acceptable to use hyperlinks instead of a full URL when space is a concern.