The default patch file viewer is messy (ie. no side by side diff view etc). I tried setting the path of beyondCompare exe in \"Settings->Unified Diff Viewer->custom\", but beyon
SVN 1.7 I think was released since this answer was posted, and I landed here because I wanted to show my newly created patch file with syntax coloring, a la view unified diff in TortoiseSvn.
It turns out that Notepad++ automatically syntax colors my file correctly if I give it the filetype of "patch"!
Patches have been around a long time but SVN is now supporting them more fully. See for example the documentation; http://tortoisesvn.net/docs/release/TortoiseSVN_en/tsvn-dug-patch.html
For how to create a patch file, see this nice document that describes various methods including mine, WinMerge; http://docs.moodle.org/dev/How_to_create_a_patch#Creating_a_patch_using_WinMerge