Go ahead and list them, at least one for every state. List your favorites.
Alabama: I just listened to one:
One Accord. Not necessarily my favorite but I'll be easy.
Alaska: Portugal, The Man
Arizona: JIMMY EAT WORLD
Arkansas: Burned Up, Bled Dry
California: Hordes obviously. I'll just say Blink-182
Colorado: Christie Front Drive
Connecticut: The World Is a Beautiful Place & I Am No Longer Afraid to Die
Delaware: Boysetsfire
DC: Uh, LOL. RITES OF SPRING
Florida: Palatka
Georgia: Portrait, I Create, Crossbearer, Circle Takes the Square...
Hawaii: I also discovered them on Dreambound,
SkyleneIdaho: Built to Spill
Illinois: Obviously a lot, but Braid and The Lawrence Arms stand out.
Indiana: The guy who booked Dude Fest was in damn near a dozen bands.
Iowa: Vidablue/Ten Grand
Kansas: The Appleseed Cast
Kentucky: SLINT
Louisiana: View of a Burning City
Maine: Aché
Maryland: The Hated
Massachusetts: Ampere
Michigan: Cheap Girls
Minnesota: Uh, hordes obviously. My all time favorite Minnesota band is probably Cadillac Blindside though.
Mississippi: See OP
Missouri: The Get Up Kids
Montana: The Sharktopus
Nebraska: Bright Calm Blue
Nevada: Curl Up and Die
New Hampshire: Transistor, Transistor
New Jersey: The entire New Brunswick scene
New Mexico: The Coma Recovery
New York: Hordes obviously but let's say Taking Back Sunday.
North Carolina: Superchunk
North Dakota: Battlefields, Tiny Moving Parts, Spirit Lies Broken...
Ohio: To Dream of Autumn
Oklahoma: Forget The Hate
Oregon: The Thermals
Pennsylvania: The Wonder Years
Rhode Island: A Trillion Barnacle Lapse
South Carolina: Hundredth
South Dakota: Edict of Milan
Tennessee: His Hero Is Gone
Texas: Mineral
Utah: Cult Leader
Vermont: Drowningman
Virginia: Owltian Mia
Washington: Sunny Day Real Estate
West Virginia: Turn Around Norman
Wisconsin: Rainer Maria
Wyoming: Teenage Bottlerocket