I like Subclipse when working within eclipse, but would like to find something better when working on files outside of Eclipse.
I'm currently using RapidSVN. Is there anything better?
Probably not what you want to hear but the command-line client is what I use and find the best outside of Eclipse. For some operations (such as branching) it is considerable faster than using Subclipse.
You may want to rephrase your question if you just want GUI clients.
Emacs has a very good SVN mode that honestly is rather usable on its own. It can be nice as well b/c you can use it in a terminal or via a "GUI" in the sense both would be available to you.
There is also RapidSVN (http://rapidsvn.tigris.org/) although, I've never used it.
I will say, that even if it is a pain, the constraint of having to use the command line tool might be a positive experience in the end. I've primarily used the Emacs mode myself, but I've found that it turned out to be a good teacher for when I've had to use the commands myself.
Ditto for the command line package. If I'm making quick edits in vim from a terminal, its much easier to stay in the terminal and use svn commit (or git, or bzr or whatever the project calls for) on the command line - if you take the time to set up the subversion config (~/.subversion/config), you can easily add commit messages and take advantages of hooks that you would otherwise have from within Eclipse (for me this entails more integration with VIM).
First of all, I recommend the Subversive svn package for Eclipse rather than Subclipse. Subversive has been adopted as an Eclipse technology project, and is (from my experiences) more smoothly-integrated.
I also tend to use the command-line tools when outside of Eclipse (and when I do, I sorely miss the SVN/CVS Synchronization Perspective that Eclipse has). I find GUI tools standing on their own to not be as useful. Unless they offer some decent features like improved interfacing to branch/merge operations, I'm more interested in tools that are integrated with Eclipse, XEmacs, et al.
The command line client is universal and, therefore, probably the best. For standalone GUI clients there are esvn and RapidSVN, KDESVN. All are essentially very similar with esvn not more developed, rapidsvn GTK based and coming from tigris (same as subversion itself) and KDESVN QT based. Selecting the best out of those is simply impossible. SmartSVN is not free, neither as in speech nor as in beer, so it is essentially no good. Subclipse and Subversive are Eclipse specific, which is heavy weight and not everybody's taste, not mine at least.
So, out of those options above I still use esvn as having the most convenient interface.
Keep an eye on NautilusSvn. It integrates with nautilus, and manages to be a pretty close analog of the acclaimed TortoiseSvn on windows.
There are a million things one can do better using a gui. So lets not make this discussion as to why someone would want to use a gui. While command line is convenient for the basics and very complex scenarios, gui is still very useful in various situations. I'll tell you what i want to do before i felt the need for a gui and stumbled upon this page.
I want to be able to view a list of commits (its possible using svn log, but the output is horrible and useless). Then, i want to be able to see what files were changed between each commit and compare different revisions. Doing this is possible through commandline, but its a real pain you-know-where.
This is just one scenario where having the facility of a gui is imperative.