dumbsvnreview is a simple tool for your code review needs. After you set it up with your repositories and your favorite graphical diff tool, specify the last revision of the most recent code review event and it'll list every changes since that have been made in the meantime. If you click on the a file then your graphical diff tool will magically pop up and you can easily see the changes.

The screenshot below should be pretty straightforward. The "diff" links open the actual diff of the revision and the links on their right will open the full diff of the file (all the changes that have been accumulated between the revision that your specified and HEAD).