I currently carry a CRKT M21 14SFG as a primary and a Kershaw speed safe tanto as a back up. I am looking for the best combat folder to use if my weapon jams.  A fighting knife should be extra strong especially in the lock. It should also have a handel designed in such a way that you wont lose your grip even when not using a thumb or pinky end hold. Im not impressed with 5.11, kershaw, crkt, benchmade, gerber, smith and wesson etc. BTW I carry a cold steel rajah when on a hike but dont feel comfortable carrying a 6 inch in public. Is there a super strong 4-4.5 inch folder out there? The CRKt doesnt look all that strong...
http://www.coldsteel.com/rajahseries.html

http://www.benchmade.com/products/760

You could look at Emerson knives.
CQC-15

You wouldn't go wrong with a Spyderco Military, Gerber Applegate-Fairbairn or a Cold Steel Scimitar.
You could consider a CRKT desert cruiser. DAMN strong and beefy.

There was a post on here recently about poor customer service with Emerson knives. Apparantly they don't like to honor warranties.

I am no fan of Emerson. I have handled/borrowed 2 of their knives. They are well made but over priced.

Ontario Knives.

Strider, Zero Tolerance, there are many others. Although when you say combat knife I think fixed blade.