Shrook is a feature rich RSS reader for keeping track of all your favourite blogs and news sites. It includes a variety of tools for managing feeds and keeping track of items you've read.
If you have multiple Macs, or an iPad or iPhone, Shrook can optionally synchronize them all, keeping the same list of feeds on each, as well as keeping track of which items (and tweets) you've read, or marked for reading later.
Shrook also includes basic Twitter support, for reading tweets alongside your feeds.