vpnc is an ipsec client for Cisco concentrators with a simple configuration file.

ipsec-tools is a command-line-only program and has a pretty steep learning curve, but it implements the ipsec standard proper and can do certificate-based, private key and xauth. You can use as both client and server, as the distinction is meaningless with ipsec.

I found armel packages for ipsec-tools on natisbad.org, install with:
wget http://natisbad.org/debian-n900/pool...7-17_armel.deb
wget http://natisbad.org/debian-n900/pool...7-17_armel.deb
sudo dpkg -i racoon-umip_0.7-17_armel.deb ipsec-tools-umip_0.7-17_armel.deb

Configuration files, you can probably find man pages online for those:
/etc/ipsec-tools.conf (policy definitions for setkey)
/etc/racoon/racoon.conf for key exchange daemon IKE (racoon)

To start manually:
sudo /etc/init.d/setkey start
sudo /etc/init.d/racoon start