I agree that LCR is probably your only bet per MS technologies. If you have an external storage shelf or a SAN you can replicate your LCR data to a separate physical medium, but as stated above you won't be able to use it until you get your primary server back up or buid a new one.
If you wanted to bring up another cheap maibox server in another site you could make it an SCR target. http://technet.microsoft.com/en-us/library/bb738131.aspx .Doubletake albeit expensive, is also another replication product.
I wanted to mention though that you can save yourself alot of frustration by not putting Exchange on a Domain Controller. If you want an all in one solution then maybe SBS is right for you.
