All summer long here at Moviefone, we've been putting together a semi-weekly series entitled Summer's Sexiest Women. (It's tough work, we know.) What we've tried to do is showcase Hollywood's leading ladies in photo galleries and video collections, hopefully helping to provide a little background on how these beautiful women came to be the eye magnets on-screen that they are today. With summer just about to wrap up, we figured it was time to choose just who is the Sexiest Woman of the Summer 2011 movie season.

Please take a moment to review the nominees:

Today we begin a weeklong tournament to determine just which stunning starlet will earn the right to be called the Sexiest Woman of the Summer. Every day this week, we'll ask you, our dear readers, Who's Sexier? By Thursday, we'll narrow it down to two finalists, and we'll announce the winner on Friday afternoon to help kick off Labor Day weekend. Sound good?

Some details: We've given our top four seeds a first-round bye. (The top seeds were determined by which posts were most popular.) They are: No. 1 overall seed Mila Kunis, followed by Jessica Alba, the women of the 'X-Men' franchise, and Olivia Wilde. Facing off today to earn the right to go up against the top seeds tomorrow are:

Hard to believe either of these two would ever be seeded second or third in a Who's Sexier? bracket, but such is the embarrassment of riches that was this summer's film season. Call this our Superheroes' Girlfriends bracket, as Natalie matched up with Chris 'Thor' Hemsworth while Blake got together with Ryan 'Green Lantern' Reynolds. Come to think of it, Thor vs. Green Lantern would be a pretty good fight ...

Who's sexier: Natalie Portman or Blake Lively?
Natalie Portman1060 (65.1%)
Blake Lively568 (34.9%)

One's a badass assassin bent on revenge; the other's a brilliant scientist -- your classic Brawn vs. Brains battle here, with beauty falling equally on both sides. Zoe's 'Colombiana' had a tough weekend competing with Hurricane Irene, while Freida's 'Rise of the Planet of the Apes' was one of the summer's most surprising hits (probably because it's really good, which was somewhat surprising too).

Who's sexier: Zoe Saldana or Freida Pinto?
Zoe Saldana1081 (68.5%)
Freida Pinto497 (31.5%)

The winner here will face off against the No. 1–seeded Women of 'X-Men' in our Franchise bracket. It just doesn't seem fair to let the Rosie Huntington-Whiteley / Megan Fox tag team compete against a solo candidate, right? The ladies of the 'Final Destination' series all met with grisly deaths, but not before gracing the screen with their considerable charms beforehand. That was one of our favorite galleries to put together, as the women of 'FD' aren't necessarily as well known as the others in this tournament, but they've got the sexiness to match up with anyone here.

Who's sexier: the Women of 'Transformers' or the Women of 'Final Destination'?
Women of 'Transformers'1126 (72.0%)
Women of 'Final Destination'438 (28.0%)

Penelope helped get things started this summer with her global smash 'Pirates of the Caribbean: On Stranger Tides,' while Rosario provided some needed comic relief with her turn in 'Zookeeper.' As much as we love Johnny Depp and, um, Kevin James, the real reasons to check out either of those flicks are pictured right there.

Who's sexier: Rosario Dawson or Penelope Cruz?
Rosario Dawson948 (59.3%)
Penelope Cruz650 (40.7%)

Check back in tomorrow to see who advanced to Round 2 to face our top seeds!

Photos: Everett Collection, GQ / Terry Richardson, Getty, Calvin Klein, Life, Maxim, Esquire, Tally Weijl, Fox, Sony, Paramount, Warner Bros., Universal.