If you are using FileMaker 13, the new "List of" summary field does exactly that.
In older versions, there are ways to use copy all records followed by a Paste, to capture the same data in a text field.
Unfortunately I am not in 13 yet.
Copy all records/request is great suggestion. First I was thinking that I need to parse out the values for the only field I need, but if I do the copy all records from a layout with that field only, the final result is the list of all values of that filed in the found set.