In each source workbook (Workbook1, Workbook2), why not add this formula in a cell right above your sets of data, to identify the workbook for each set. Example:

In Cell A1 of Workbook1:
=cell("filename")

Then, in your summary file, link to Cell A1 in Workbook1, in order to pull that workbook's filename.

Do this for each set of data in your Summary.xls

This may not be the solution for you, though, as I did not understand this: "The missing element for me would be to have in the summary workbook a column that display the file name display in that fx area so I don't have to look up every cell to double check if I actually paste the right thing at the right place."

If what I suggested DOES work for you, then the caution is, using a link to a cell like this can be vulnerable to typos. You might copy data from Workbook2 into your summary.xls, but then accidentally grab a link to a different set of data in Workbook1.