So a co-worker's father just died and he haf a gun collection.  My co-worker is not 100%  sure what he has but it sounds like Viet Nam era stuff and newer.

He would like to get the collection appraised. Any recommendations?

Make a list of make and models, finish condition (not really indicative of overall condition) then look on Gunbroker for the prices they bring. It is not necessarily what you will get when you sell them, but it will give you a guide. It could be more or less.
Tell them to be careful, lots of thieves in the gun business. Get second opinions...
I've seen ridiculous prices asked for old guns just because they were old. I also know of people being ripped off on selling them to "friends" helping them out, who promptly resold the gun for a big profit.
How big is the collections?
Post pictures here of the collection and someone may awake from their graves to help.

I agree, you could post pics and info on them here and get helped.  I'm curious to see them also.  If you just really want a professional appraiser I'd contact some of the shops around town, such as Wilshire Gun/Cold Hand Arms and H&H, and ask if they can recommend someone.  I know H&H buys and does consignment on a lot of guns from the 1800's to today so they gotta have someone who does their stuff for them.  It's an idea anyway.

David at 7 Element in Moore offers consignment as well.

As does Tommy at Sooner State Pawn (S. OKC) and his manager Darren at Sooner Guns and Gold (Norman).

Do you need a professional appraisal or just a honest idea of what they are worth?