I really love the TortoiseSvn diff software. I can download them standalone as a zip, but I really love when iI can select two files and then right click and from context me
I needed something similar (just a standalone app to make diff files) and was able to copy the following out of the Tortoise install directory (C:\Program Files\TortoiseSVN\bin\) to make TortoiseMerge work on its own (similar to the accepted answer's suggestion). Maybe extract them from the full installer if you don't have it installed already?
As far as the context-menu entry:
myprogrampath\path\path\executable.exe %1 %2)