I'm kinda good with this stuff, but I assume you mean bands that sing and then scream, and the whole metalcore genre, not actual hardcore and screamo bands (because the first reply you got isn't really...the catchy stuff I think you're looking for. I mean it's really good stuff but doesn't exactly sound like the stuff I think you're going for).
Anyway, I know some of these were mentioned already but oh well.
Every Time I Die--Ebolarama, She's My Rushmore
Norma Jean--The Entire World is Counting On Me..., The Shotgun Message
Zao--The Last Revelation, Truly, Truly, This Is The End
Fear Before The March of Flames--too many good songs to name, but take these ones: On The Bright Side, She Could Choke, The State Of Texas Vs. Fear Before, and Should Have Stayed In The Shallows
HORSE the band--can't miss this band, everyone calls them Nintendocore

, check out: Sevententacles and Eight Flames, and Bunnies
From Autumn To Ashes--Take Her To The Music Store should hook you, but also check out The After Dinner Payback and Short Stories with Tragic Endings
Lastly, because I know I am running out of bands to name, Haste The Day, check out Substance and Blue 42.
But I do better with the shitty mainstream HH-MCR type of bands, so I have a lot more to recommend in that category.
From First To Last- Ride The Wings of Pestilence. Enough said.
Underoath (the band's new cd) - Young And Aspiring, A Boy Brushed Red, Living In Black And White, I'm Content With Losing
Emery - Walls, they also did a good cover of "Holding Out For a Hero"
The Receiving End of Sirens - Planning a Prison Break, The Rival Cycle, Broadcast Quality
Senses Fail...catchy stuff here, I wish I could name all their songs, but check out Stephen and Free Fall Without a Parachute, and then Tie Her Down, Buried a Lie, and You're Cute When You Scream.
Matchbook Romance - horribly generic band, but I'll list anyway. Promise and Your Stories My Alibis are two good songs.
Emanuel - Just get their new cd. Every song is great.
A Static Lullaby - The Shooting Star That Destroyed Us All, Radio Flyer's Last Journey
Across Five Aprils - sadly I can't think of any of their songs.
Atreyu - The Crimson, Bleeding Mascara, Lipgloss and Black, Tulips are Better
My American Heart - Don't Sleep, This Won't Stop, Maps around Texas.
I assume you've already heard of Thrice and Thursday, but if you haven't, they're a must-listen-to, mainstream wise.