In Hollywood, July and August are hotter than Hades, as are the red carpet arrivals at some of the summer's biggest movie premieres. But, while some stars sizzled, others fizzled. Click ahead and see.

Photo by John Shearer/WireImage.com, WireImageAngelina Jolie
"Inglourious Basterds" LA premiere
Grade: A

Angelina Jolie made a triumphant return to the red carpet at the premiere of her partner Brad Pitt's latest film, "Inglourious Basterds," in a black strapless leather dress courtesy of Michael Kors.

Photo by Jason Merritt, WireImageCatherine Keener
"Ponyo" LA screening
Grade: F

Catherine Keener's unruly mane and pocketed white tent weren't just unflattering, they were downright failures.

Photo by Jim Spellman, WireImageEmma Watson
"Harry Potter and the Half-Blood Prince" NY premiere
Grade: A+

Emma Watson stole the spotlight at "Potter's" New York premiere in a divine Proenza Schouler dress, highlighted by a black halter bodice.

Photo by Jon Furniss, WireImageHelena Bonham Carter
"Harry Potter and the Half-Blood Prince" London premiere
Grade: D+

Helena Bonham Carter solidified her status as a hot mess in a disheveled getup and disastrous 'do.

Photo by Stephen Lovekin, Getty ImagesClaire Danes
"Taking Woodstock" NY premiere
Grade: A

Thanks to the blue silk Sonia Rykiel Resort 2010 wrap-dress she sported to a screening of "Taking Woodstock," Claire Danes easily earned herself an A.

Photo by Junko Kimura, Getty ImagesSienna Miller
"G.I. Joe: The Rise of Cobra" Tokyo premiere
Grade: B+

The sultry Sienna Miller took Tokyo by storm at the Japanese premiere of her actioner in a sleek Gucci suit, midnight blue blouse, and peep-toe platform booties.

Photo by Dave Hogan/Getty Images, Getty ImagesKatherine Heigl
"The Ugly Truth" London premiere
Grade: A-

Katherine Heigl was captivating at the London premiere of her rom-com in a glittering green Naeem Khan one-shoulder belted sheath and metallic accessories.

Photo by Jim Spellman, WireImageDaniel Radcliffe
"Harry Potter and the Half-Blood Prince" NY premiere
Grade: D-

Daniel Radcliffe looked painfully awkward as he channeled the Tin Man in a stiff silver suit.

Photo by Don Arnold/WireImage.com, WireImageDiane Kruger
"Inglourious Basterds" Syndey premiere
Grade: A+

While in Australia promoting "Inglourious Basterds," Diane Kruger dazzled in a draped Marchesa dress and crystal-encrusted Christian Louboutin heels.

Photo by Jim Spellman, WireImageRachel McAdams
"The Time Traveler's Wife" NY premiere
Grade: C-

Unfortunately, the adorable Rachel McAdams dared to bare a lil' too much skin in a shoulder pad-enhanced Emilio Pucci ruched dress, which featured an extreme plunge.

Photo by Jemal Countess, Getty ImagesRenee Zellweger
"My One and Only" NY premiere
Grade: A-

Renee Zellweger attended a special screening of her new film, "My One and Only," sans rumored beau Bradley Cooper, in a fabulous one-shoulder Carolina Herrera frock and nude heels.

Photo by Jon Kopaloff, Film MagicAmy Adams
"Julie & Julia" LA premiere
Grade: D+

Love me some Amy Adams. Hate that her bra strap was showing and that she didn't bother to wash her hair before hitting the red carpet at the West Coast premiere of her latest chick flick.

Photo by Steve Granitz/WireImage.com, WireImageChristina Ricci
"Inglourious Basterds" LA premiere
Grade: A

Is it just me, or was Christina Ricci looking better than ever at the "Inglourious Basterds" kickoff? Her fire engine red frock, sharp bangs, and $800 Christian Louboutin "Bianca" pumps were simply perfect.

Photo by Jamie McCarthy, WireImageLindsay Lohan
"Inglourious Basterds" NY screening
Grade: F

Lindsay Lohan's fall from grace continued as she took her newly plumped lips and ratty hair extensions out for a night on the town.

Photo by Sean Gallup, Getty ImagesBrad Pitt
"Inglourious Basterds" Berlin premiere
Grade: B

Brad Pitt would have achieved a better mark had he ditched that grizzled goatee. But, he did look undoubtedly dapper in his Tom Ford suit.

Photo by Michael Buckner, Getty ImagesRumer Willis
"Spread" LA premiere
Grade: C

Rumer Willis delivered yet another blah red carpet moment in a metallic Karen Millen clunker and Christian Louboutin heels.

Photo by Jesse Grant, WireImageEmmy Rossum
"Orphan" LA premiere
Grade: A

When did Emmy Rossum become a sexy style standout? The actress dressed to impress at the thriller's opening in this slightly gothic and totally hot Phi fall '09 high-neck dress.

Photo by Jon Kopaloff, Film MagicMilla Jovovich
"A Perfect Getaway" LA premiere
Grade: C+

Milla Jovovich is magnificent. Unfortunately, her goth makeup and sharp 'do didn't go with her angelic summery frock.

Photo by Dimitrios Kambouris, WireImageRose Byrne
"Adam" NY screening
Grade: B+

At a New York screening of her sensational new film, Rose Byrne successfully rocked a Christian Cota turtleneck dress, Bottega Veneta jewels, Brian Atwood patent pumps, and a metallic Max Azria clutch.

Photo by Jon Kopaloff, Film MagicMeryl Streep
"Julie & Julia" LA premiere
Grade: C

Meryl didn't bring her A-game to the "Julie & Julia" premiere in a dull but decent outfit. Then again, she never does. Sad, but true.

Photo by Jon Kopaloff, Film MagicKate Walsh
"The Ugly Truth" LA premiere
Grade: A

"Private Practice" hottie Kate Walsh wowed the crowd in an Isabella Oliver-designed sleeveless blazer and shorts, which she paired with gold accents, including a pair of Moschino peep toes.

Photo by Ethan Miller, Getty ImagesHolly Madison
"The Goods: Live Hard, Sell Hard" Las Vegas premiere
Grade: D+

Wearing a Greg Barnes creation from the adult production of Peepshow made the former Playboy Playmate look like a wretched woodland nymph.

Photo by Mark Von Holden, WireImageLeighton Meester
"(500) Days of Summer" NY screening
Grade: B+

The mesmerizing Leighton Meester pulled off a daring fashion decision en route to a screening of "500 Days of Summer." The "Gossip Girl's" purple and red houndstooth Emilio de la Morena shift dress and $750 Alexandre Birman python booties were simply stunning.

Photo by Frazer Harrison, Getty ImagesSara Paxton
"Spread" LA premiere
Grade: F

Sara's matronly ensemble, featuring a cream and gold jacket by Elise Overland and objectionable booties, would've made much more sense on Blanche Devereaux, not the red carpet.

Photo by Frazer Harrison, Getty ImagesRachel Nichols
"G.I. Joe: The Rise of Cobra" LA premiere
Grade: A-

"G.I. Joe's" breakout star Rachel Nichols popped a pose in a fierce one-shoulder Franco Kaufman jersey dress upon arriving at her premiere.

Photo by Jordan Strauss, WireImageNiecy Nash
"G-Force" LA premiere
Grade: B+

Niecy Nash garnered herself a more-than-respectable B+ by wearing a beautiful black and white hip-hugger and matching peep toes to the kiddie comedy.

Photo by Jesse Grant, WireImageVanessa Hudgens
"Bandslam" LA premiere
Grade: B-

Zac Efron's main squeeze is super cute, but her Georges Hobeika dress is a little too similar to the Moschino frock she sported to the Japanese premiere of "HSM 3."

Photo by Jun Sato, WireImageChanning Tatum
"G.I. Joe: The Rise of Cobra" Tokyo premiere
Grade: A

The hunky Channing Tatum set hearts afire in a navy blue "New Manhattan" herringbone suit courtesy of Gucci.

Photo by Steve Granitz, WireImageDemi Moore
"Spread" LA premiere
Grade: B+

Demi Moore looked mighty fine in a lavender Louis Vuitton dress and multi-colored Giuseppe Zanotti heels.

Photo by Jesse Grant, WireImageVera Farmiga
"Orphan" LA premiere
Grade: A-

Vera Farmiga was positively radiant in a silk one-shoulder Versace gown. She completed her look with a classy updo, a metallic clutch, and leather sandals.

Photo by Kevin Mazur, WireImageElizabeth Banks
"Funny People" LA premiere
Grade: C-

Ms. Banks' lovely MaxMara LBD was overshadowed by her back-combed coif, which resembled a lion's mane.

Photo by Chelsea Lauren, WireImageSienna Miller
"G.I. Joe: The Rise of Cobra" LA premiere
Grade: A-

Sienna Miller channeled Old Hollywood at a SoCal screening in a glamorous gold Yves St. Laurent gown, cherry red lips, and wavy 'do.

Photo by Jon Furniss, WireImageRihanna
"Inglourious Basterds" London premiere
Grade: C-

Rihanna borrowed Madonna's look from 1983 at the British debut of Quentin Tarantino's latest. Her black Alexander McQueen jumpsuit, layered pearls, lace fingerless gloves, dark shades, and matching Maison Martin Margiela heels were undoubtedly Material Girl-inspired.

Photo by Jason Kempin, Getty ImagesMichelle Monaghan
"Inglourious Basterds" NY screening
Grade: C+

"Eagle Eye" star Michelle Monaghan paired a structured navy Rachel Roy dress with a chunky cuff and distracting Manolo Blahnik strappy sandals.

Photo by Frederick M. Brown, Getty ImagesKatherine Heigl
"The Ugly Truth" LA premiere
Grade: B+

Katherine Heigl was the opposite of ugly at the Los Angeles premiere of "The Ugly Truth," in a strapless tulle Lanvin frock, chunky David Yurman pearl necklace, and matching metallic heels.