Remmina - The GTK+ Remote Desktop Client  v1.4.33
Remmina is a remote desktop client written in GTK+, aiming to be useful for system administrators and travellers, who need to work with lots of remote computers in front of either large monitors or tiny netbooks. Remmina supports multiple network protocols in an integrated and consistent user interface. Currently RDP, VNC, NX, XDMCP and SSH are supported.
Remmina-SSH-wizardry

When the SSH tunneling features are not enough, you can work around it with other Remmina functionalities, like the pre and post commands in the "Behavior" tab, or the SSH proxy command for SSH connections.

SOCKS proxy connection

In this example, before connecting to the remote server, a SOCKS tunnel is created, and closed when the Remmina connection ends.

ssh config

Host foosock
User foo
Hostname foorealserver
ControlMaster auto
ControlPath ~/.ssh/cm_sockets/%r@%h:%p

remmina

precommand=/bin/ssh -fn -N -D 9090 foosock
postcommand=/bin/ssh -O exit foosock