What the font: the letter i used in Apple's information button
Hoefler Text Bold Italic

http://www.typography.com/fonts/font_styles.php?productLineID=100010



It was designed for Apple:


  Hoefler Text is a contemporary serif Antiqua font that was designed
  for Apple Computer to demonstrate advanced type technologies. Hoefler
  Text was created to allow the composition of complex typography; as
  such it takes cues from a range of classic fonts, such as Garamond and
  Janson. Designed by Jonathan Hoefler in 1991, a version of Hoefler
  Text has been included with every version of Mac OS since System 7.5.