I use NetNewsWire to read all my feeds. One of the great things about it is that you can use custom CSS styles. Antonio over Aisle One has put together a wonderful set of NetNewsWire styles that he calls Legistyles. As he mentions on the Legistyles site “Much attention has been paid to the design and typography of the styles to improve legibility and readability, and to enhance the overall reading experience.”
Currently there are 4 styles available.
Serif Black 1.0, Serif White 1.0 (Titles and body text are set in Baskerville)
Haaus (Titles are set in Futura and the body text is set in Lucida Grande)
and Brockmann (Titles and body text are set in Helvetica)
Check it out for yourself here.