Contact Sheet Automation

How about this javascript?

if (app.selection == null || app.selection.length < 2)
{
  alert ("Please, DO select just an empty text frame and one or more images...");
} else
{
  filelist = '';
  textframe = undefined;
  for (i=0; i<app.selection.length; i++)
  {
    if (app.selection.hasOwnProperty("contents"))
    {
     if (textframe != undefined)
     {
       alert ("That's more than a single text frame. Seriously.");
       exit(0);
     }
     textframe = app.selection;
    } else
    {
      if (filelist == '')
        filelist += app.selection.images[0].itemLink.name.replace(/\..+$/, '');
      else
        filelist += '_'+app.selection.images[0].itemLink.name.replace(/\..+$/, '');
    }
  }
  if (textframe == undefined)
    alert ("Got a lot of stuff but no text frame?");
  else
   textframe.contents = filelist;
}

Select a text frame along with one or more images and run the script. The text frame will be emptied, and the list of image file names sans extension will magically appear inside it, separated by underscores.

Copy, paste into the Extendscript Toolkit Editor that came with InDesign, save as "GrabImageNames.jsx" into your Scripts folder. When saved in the correct location, ID will immediately show it in the Scripts panel.

[Edit] Added a final check for a valid text frame somewhere in the selection. :-P

[Edit #2] Damn my busy brain. Additional note: it will only work with bitmap images -- TIFF, GIF, BMP, JPEG (PSD?), not with AI, EPS, PDF, WMF. Additional note #2: it mercilessly slices off everything after the first period, so if you may have filenames that contain multiple periods, scream and I'll take a look.