Mike, thats a great question and one many many of us have come across, and I think its a real landmark when you do.
I generally have 3 rules of thumb. Number 1, NO ONE gets free photos - exception, my wife, sister, mum and dad, nikki's brother.
Number 2. If you want the rights to my photos you pay the full price unless you are covered by rule3. The full price of the photo in my case means either a print price or my 1/2 day rate or a full days rate. I also NEVER let images go out untouched by me first and I ask them what sizes they want and do the post processing. Typically if you only want one photo for a magazine, I will supply it in A4/8x12 size, 4x6 size and 2x3 size - this will cost you (if its an image I shot for someone else example - at a concert, and its a bacground photo, groups scene at a football game or something like that) - the cost for the image with non exclusive rights £150.00 If its a photo I shot while working for you, its covered by the original contract.
Rule 3 - Whats in it for me ? - Yesterday a guy I know very well, (I do a lot of networking groups like BNI etc.) This guy is a BNI chapter director, has a lot of connections and has and can open a lot of doors for me - He wanted a shot I have of him for a publicity campaign. I am supplying him the photo for £50.00 - in the 3 sizes listed above - I could have done it for free but I am a firm beleiver in if you give away your WORK for free, the person will see little or no value in it - I will rant more about this later.
So to answer your question quickly. Either A, give it to them (I never do) B. charge them a fair rate for limited use of the photo or C, if they can do something for you, make a nominal charge for your time etc.
P.S. I do from time to time work for some very large companies over here in the UK, If they need a job doing that I could do for free and could do easily, I will do it but ask them to make a donation of £25.00 to one of the charity's I do work for. I have never had one say NO or seem shocked to be asked to do this, it also have worked well for me because later talking to them it built up my respect level with them somewhat.
Last but not least - DONT be afriad to quote a price, they will either pay it or say its too high - if its too high, you can always come down but you can never go up !