Well, you can use git and git-svn. First, clone your SVN repository into a Git repository, like this:
git svn init "http://host/repo/location/trunk"
Then, use the command:
gitk --all
From there, you'll see a nice graph of the revision history. Of course, this assumes you have git and git-svn set up correctly and are comfortable on the command line.
One of the benefits of tracking source through Git is that the merging history is tracked through content modification, not chronological order or branch name. Therefore, it doesn't matter if your SVN repository has no merging history.
If the gitk revision graph isn't sufficient, you may be able to pull the repo history from Git directly and make your own graph.
