Flexible Renamer is easy to use. Just pick a directory where your files are on the left, select the work that you want to do to your files from the middle, and check in the right window to make sure that your files are going to be renamed and directed the way you wish. Click 'Rename' and volia, your finished. The program is really fast too as I have changed up to 175 photo file names in one session with a total time used at approx. 15 seconds. As shown, you can change the name in any number of combinations such as the Date Time (default), strings (words that will be on all files), adding numbers to the beginning/end of any string plus more. You can set the number of digits in the filename (excellent for naming over 100 pics to keep them in order, such as 001!), and even the start number. This is very handy if you are combining bunches of pics from different directories to one directory. The window can be expanded to show you quite a bit of information including a list of the files after they have had their names change. The column's are adjustable, as are the individual windows for each specific area.
Along with all of the above goodies, Flexible Renamer can also copy and rename to another folder, has an undo feature, allows the use of wildcards, and has a multiple file filter. Here's a pic of the 'context menu option' window with all of the possible settings:
