Additional (from the rich and famous):

"I don't regret cheating; it helped me change my ways."

"I needed some alone time."

"I did not have sexual relationships with that woman."

"It depends on what the nature of the word "is" (re: sexual relationship) is."

"I felt bad for the prostitute/transvestite, etc. because he/she was crying, and helped them by emptying out my wallet."

"I get a headache if I don't have sex every three days."

"Sex is best when cheating."