Almost all Linux distribution comes with its own set of GUI tools to manage users and groups. For example:
* Red Hat comes with redhat-config-user
* Suse comes with Yast
* Debian Linux and other distro come with users-admin GUI tool set
* FreeBSD with sysinstall
* Solaris comes with Solaris Management Centre (SMC)

However, I recommend managing user accounts from command line. It offers following benefits over GUI tools:

• Using commands from command line is faster
• Automation is possible as per your requirements (use of Perl or shell scripting)
• If you are going to use LDAP or NIS then command line provides best solution as compare to GUI tools