What corporations, either based here or with major or medium presence will sponsor the NHL team or any other major league team in Oklahoma City?

Sonic, US Cellular, Bud-wise-er, Southwest Airlines, Dell computers come to my mind.

What about small companies?

Just for argument's sake, I'll throw in these names:

Devon Energy
Chesapeake Energy
Express Services
Cox
Gaylord Entertainment/The Oklahoman
Bank of Oklahoma
Crowe & Dunlevy

Kerr McGee
Ford
GM
Benham
BOK Financial
Bank of Oklahoma
Chase
Local Federal
BankFirst
UPS
FedEx
OGE Energy
ONEOK
AT&T
AT&T Wireless
SBC
Dobson Communications
The Boeing Company
Dillards
Federated Department Stores "Foley's"
American Airlines
Hertz

While many of these corporations do not have their worldwide corporate headquarters here (althought some do), most if not all have some sort of regional hq and/or significant operations in Oklahoma City (and especially downtown).

I am sure many of these companies are forgotten but are really the corporations that sponsor wherever they have regional hq (like here), national hq, or significant operations.

I think you guys pretty much covered everyone! I guess the top ones I would've listed would've been Sonic, Kerr McGee, Gaylord, Express Services, Devon, Chesapeake, OG&E, Cox Communications, SBC, etc. They always seem to be the ones that jump in when support is needed.