Flip through the slideshow below for 20 songs that are essential for any Britney Spears playlist, from her 1999 debut "Baby One More Time" to later favorites like "Till The World Ends." ...

Just when you thought 1999 was the greatest year in pop music—thanks to debut singles by Britney Spears and Christina Aguilera—here comes 2000 to throw down the goods. If the late 80s and early 90s ...