There are a lot of header manufacturers today, here is a list of those I know of for the 99-2007 Classic style trucks ...
Longtubes and midlength...
Honorable mention for OBS conversion guys ... site sponsor Schoenfeld Headers
Pacesetter
OBX
HOOKER
TOGs - The Other Guys
AZSM - Arizona Speed and Marine
LPP - La Monte Performance Parts
Doug Thorley
Dynatech
StainlessWorks
American Racing Headers
Shorties...
Edelbrock
Hedman
Dynatech
LPP
BBK
JBA
Doug's
Gibson
Borla
SLP
Feel free to add others you know of or correct the names I have listed
For 2007+ engines...
American Racing Headers
SLP - shorties
ELECTRIC CUTOUTS manufacturers
from DamnYankee...
The DMH has a 4 year warranty and is $199 shipped
The QTP has CRAP reviews has a 30 day warranty and is about $190 shipped.
The RaceReady has good reviews has a limited lifetime warranty and is about $260 shipped.
Those are about the only manufacturers.