Update June 2011: The greatest disappointment I have in the tv version of this epic story is the casting of Cersei Lannister. She is supposed to be this sexy diva who is a conniving bitch. Leana's portrayal of Cersei doesn't even scratch the surface of the character. She's too subtle, rigid and the most she can do to look evil is smirk. I don't know what it is about this actress but she lacks expression or is not animated enough in her movements. Plus her tone doesn't change much, there's no highs or lows - no depth.
Angelina Jolie would have been the perfect Cersei Lannister, but let's face it - her name is too big, she's too expensive and too busy to commit to years of tv even if it's something as awesome as the Game of Thrones.
Cersei is the twin sister of Jaime Lannister and matches his beauty, with golden hair and bright eyes. After Robert's Rebellion she married the new King, Robert Baratheon, and became Queen of the Seven Kingdoms.
Cersei has shared an incestuous relationship with her brother Jaime since they were youths, and continued it throughout her fifteen-year marriage to King Robert, made possible both by Cersei's craftiness and Robert's philandering nature. Her three children Joffrey, Myrcella and Tommen, were all fathered by Jaime, rather than her husband; this secret, when discovered by Jon Arryn, Eddard Stark and Stannis Baratheon, was used as a political tool during the War of the Five Kings.
I imagined Angelina Jolie to play the often bitchy and conniving Cersei Lannister in A Song of Ice and Fire epic novel series.