Subversion --diff-cmd and diff3-cmd switches
--dif-cmd and GNU diff
By default, subversion uses it's internal diff to generate output for the diff subcommand. This works great for generating patches, but can difficult to read. By supply the --diff-cmd switch, you can tell subversion to use an external diff engine like 'GNU diff' and thereby get some more readable results.
Side-by-Side diff
svn --diff-cmd "diff" --extensions "-y" diff
--diff3-cmd
By using the diff3-cmd switch, you can tell subversion what shell command to use for merging. This could be a good place to make some groovy (or rather groovy groovy) script hooks into the merge process.