Who knows an easy to use IPsec Client for windows

Windows have pptp/ipsec client already available. Although it might be broken on some systems. For instance when using ipv6 and other causes such as, but not limited to wrong configuration. I use l2tp-ipsec in order to connect from home to the office workplace without any problems.

What are you trying to accomplish?

If you're attempting to vpn from a workstation, I'd highly recommend looking into OpenVPN rather than using IPSec. It still provides excellent security, but is easier to configure and works better in dynamic environments imo.

Hamachi or OVPN are good free solutions, but OVPN installer looks little bloated and really not easy to configure for the end-user. With not easy I mean as the VPN client that comes default with Windows.

Lucky in time OVPN will release package to enroll a customized client. That can be send to the end-user with minimal configuration on their part. I tried OVPN and it worked better then i'd expected. Though DNS on Windows might be something to take care. If plan is to use this VPN as anonymous service for non experienced end-users.

Then again. I'm not a security expert.