Araxis is by far the way to go. I’ve used a lot of various compare/synch programs over the years and it is by far worth the extra few bucks.
on Mac, there is still ECMerge (http://www.elliecomputing.com/) with a native version. not free though ($US 30)
There is a list of free alternatives for the linux folks which are reviewed here http://www.amjith.blogspot.com/2007/07/visual-diff-tools-in-linux.html
I recently evaluated diff/merge tools. So far the best alternative to BC on Mac seems to be DeltaWalker http://www.deltopia.com/compare-merge-sync/
Its multiplatform (Mac OS X, Windows, Linux) like ECMerge, but it has a much cleaner interface. Before I used KDiff3, but with DeltaWalker synchronization even of huge folders is now plain easy.
Have you tried WinMerge (http://winmerge.sourceforge.net/) - it’s got the best license cost of all - $0. I’ve been using it for several months pretty happily.
Beyond Compare is the best utility,I been using in for some time now,there is also,UltraCompare Professional from the makers of UltraEdit I test that too…but think BC is better in some ways…didnt compare the prices of these two though…
A wonderful and simple diff tool is kompare for KDE.
Being part of kde it treats remote files on ftp servers etc the same as any local file. And of course is free.
Compare++(http://www.coodesoft.com/) is one of most intellectual diff tool. It can detect function changes and generate HTML and text report. A good feature is “Function View” which can visually display the difference between two versions of source code.
Here has a demo: http://www.coodesoft.com/videos/video_report.html
BeyondCompare is my favourite merge tool. However, a great free tool is Perforce Visual Merge which is part of the P4V Suite: