Klein's book "Politics Lost" is a fascinating look at his view of some of the problems in the American political process. To this end, the sub-title of the book "From RFK to W: How Politicians Have Become Less Courageous and More Interested in Keeping Power than in Doing What's Right for America" offers a good preview of his feelings on many elected officials... and the political consultants and handlers who shape those officials.
One thing of particular interest in the book is Klein's mention of Robert F Kennedy's speech (overviewed and available in this NPR story) the night of Martin Luther King Jr's assassination. Kennedy's unrehearsed (and now famous) speech to a largely black crowd on this extemely emotional and volitile night is held up by Klein as an example of the best that political leaders can and should offer the public.
While Klein has garnered a good amount of attention for his books, he is also well know for his frequent commentaries (named after the famous "Man in the Arena" quote from Theodore Roosevelt) in Time Magazine.
Several of Klein's commentaries that I've found to be of note are those on Merle Haggard returning to the Democratic Party, Tim Russert and his relationship with Klein and Barack Obama's Cabinet choices should he become President. That said, Klein has a breadth of excellent writing and his "In the Arena" work can be found at this compilation list.