Alyson Hannigan Pictures

Although more mainstream in recent years, Alyson Hannigan is a life-long actress who currently plays Lily Aldrin in "How I Met Your Mother." Alyson is also known for her previous roles as Willow Rosenberg on the hit television series "Buffy the Vampire Slayer," Julia Jones in "Date Movie," and of course the quirky and perverted flautist Michelle Flaherty in the "American Pie" film series.