I think we all have been in a situation where someone wants to use your image, but they cannot pay you. Instead they offer you a credit or experience or something great for your portfolio.
In the following video, Matt Granger suggests that you stop giving out your work for free.
[Rewind: Does Working For Free Ever Pay Off?]
The question you need to ask yourself is “Should I Work For Free?” I volunteer my skill to a veterinary hospital and to a local music school and I do not demand any sort of compensation for the work. This is not the type of situation that Ganger talks about; it is where well-to-do companies ask for your work for free when they can easily pay for it. If a company values your work enough to use it as part of their advertising campaigns and/or promotions, a monetary compensation should be able to back that value.
There are photographers who will easily give their work away for credit or exposure, but is it worth it? Exposure is good in the beginning, but when do you draw the line? Does any other professional give out their work for credit/free? Can you go to a restaurant and tell the chef that you cannot pay them, but you will tell all your friends how good the food was? You would either be kicked out or laughed at and sent to the back to wash dishes.
Giving out your work to be published is okay once and awhile and you may even see some-sort of compensation from it. There is a flip side of the coin however, giving away work to established organizations then demanding reimbursement after the fact can come back to bite you. You should know how your work will be used beforehand and set your compensation accordingly.