Whats the difference between....?

Whats the difference between a Ford Taurus SE, SEL and SES?? I have a 2000 Taurus SE and I think the SEL and SES mean they came with other factory options, but what are they?? My Taurus has pretty much everything (CD changer, power everything, cruise control) so I don't know what the differences could be. Anyone know?? Thanks!