Feed Rinse is not a source of additional content, it is a tool that can be used to filter out things from an existing feed like you can filter out bad language or keywords. So if you find a feed that you want to consume on your site but are afraid it might include some content you don't want you can run the feed through Feed Rinse and use the output feed url from Feed Rinse to get a sanitized version of the feed that you can consume.
There are lots of feeds on the net that you could consume on your site if they have relevant content but you'll have to do your own searching for them.
Feed Manager is a tool that can aggregate feeds from multiple sources into your site.
Lots of people also subscribe to feeds using Feed Readers such as Google Reader which I use myself to subscribe to about 100 or so technology blogs.
Hope it helps,