Truecrypt is pretty handy. At this point in time the use of cryptography in the court room really impacts the case.
Truecrypt and other hard drive encryption schemes are generally vulnerable to something called a "Cold Boot Attack". Basically, when a hard drive is fully encrypted the password is stored in memory while the computer operates. Once the computer turns off the password is overwritten.
The coldboot attack is a physical attack where the computer is cold booted and the attacker can flash freeze memory in order to preserve its state for a longer duration.http://en.wikipedia.org/wiki/Cold_boot_attack