This is the best and most native Rated 5 out of 5 stars
download-helper addon I can think of. Some users might consider it as confusing to see all those cached items, but I prefer this kind of addon because it uses a really reliable way to get it done. Furthermore I believe that many users just do not know that all visible (or audible) items have already been downloaded to their computer. So they just need to extract them from cache. CacheViewer does that work perfectly.
However, I was wondering why many cache items are declared to be stored on disk while the detailed information says 'File on disk: none'. According to MDC information, I found that those items may be stream-based. If so, please add this information in an coming version.