I don't think you're going to find a type of RAM that is secure against cold boot attacks.
It may be possible to build application-layer defenses against this, by ensuring that all sensitive data stored in memory is stored in encrypted form. Then when you shut down, you simply need to securely overwrite the decryption key. However, this is likely to have significant performance and implementation costs, and I would question whether it is worth it.
I think you need to do some serious introspection to determine whether the cold boot attack is really a likely attack against your system. Security always needs to be directed by deliberate risk management. With some risks, the best approach is simply to accept the risk. Alternatively, you may be able to mitigate the risk by providing physical security. For instance, if you have super-sensitive data, perhaps you don't want to store it on a machine at a colo facility: perhaps you should keep it on a machine on your own premises.
If you want to tell us more about your specific application needs and scenario, and share the risk analysis you've already done, we may be able to provide more concrete suggestions. But for now, my initial reaction would be to suspect that you're over-thinking it: for most people, the cold boot attack isn't really worth worrying about.