web server failover

[unre4l]

Does anyone have any recommendations on how to do a web server failover in an emergency situation. We have an offsite dns server that can do name resolution. The offsite and onsite are two different networks with different ip ranges. Now in the case everything onsite is down, we will still have the offsite dns server that can do name resolutions but we will have to bring our offsite web server with a different ip and change the dns entry so that it can propogate.
Has anyone used some sort of dynamic dns service or any other ways to accomplish this?