My favorite diff tool (and it does so much more) for a long time has been Beyond Compare.
When I started using SVN and Eclipse - I looked for a way to integrate Beyond Compare into the mix so I could use it to compare my working copy against the repository. I found Beyond CVS - but unfortunately it only supported CVS. :( There were a few comments on there asking for SVN support and I added one myself and promptly forgot about it.
Well a few days ago I got an email from the plugin author informing me he had finally updated things and added support for SVN!!! Woot!
To install - simply download the ZIP (make sure you grab the one with SVN support!), extract the ZIP and copy the /features and /plugins directories to your existing Eclipse directory.
Crank up CFEclipse and you should have some shiney buttons as well as some additional options in your right click menu when you go to compare a file:
UpDate: Looks like the new 0.8.x version requires Eclipse 3.4.