GUI SVN client for Debian Linux

RapidSVN is a pretty decent multi-platform client.

Seen a bunch. Officially declare: command line is waaay more effective, and naturally integrates with other GNU utilities. Learn the command line! :) It's free, visual, and very good. And it's simpler than it seems.

KDESVN A feature-rich client with great history and revision views, annotated code views showing who changed each line of code and when it was changed, and 3D graphical views of branching and merging among trees. Written in C++ with Qt, but using KDE libraries (which are somewhat troublesome to get on Windows).

Unfortunately, the developer of KDESVN stopped the development and is shutting down its track website in summer 2012 (EDIT: he resumed development of maintenance releases in June 2012).

RabbitVCS A Python extension to integrate Subversion functionality into the Nautilus File Manager, basically as a clone of the TortoiseSVN project on Windows. —Wikipedia

SmartSVN is very useful. It is shareware, but after 30 days you still can use limited edition and it still remains effective.