Some beginning books about relativity:

Albert Einstein, Relativity: The Special and the General Theory (1917; reprint by Crown)

Robert Geroch, General Relativity from A to B University of Chicago Press)

Robert Wald, Space, Time and Gravity (University of Chicago Press, 1977)

E.F. Taylor and J.A. Wheeler, Spacetime Physics (Freeman, 1966).

Kip Thorne, Black Holes and Time Warps: Einstein's Outrageous Legacy (Norton, 1994).
 

Einstein as a philosopher:

P.A. Schilpp, editor, Albert Einstein, Philosopher-Scientist (Open Court)
 

Books about Einstein's life:
 

Jeremy Bernstein, Einstein (New York: Viking, 1973).

Philipp Frank, Einstein: His Life and Times (Knopf, 1972).

Roger Highsmith and Paul Carter, The Private Lives of Albert Einstein (Faber, 1993).
 
 

A useful website:

www.physics.syr.edu/courses/modules/LIGHTCONE/