Truecrypt is nice, but it is not regarded as true FLOSS application.

Scramdisk for Linux – SD4L is an alternative, licensed under GPL and is compatible with Truecrypt containers.

However, as the name suggest this is available for Linux not for *BSD. The interface is not as intuitive as Truecrypt, but gets the job done.

Compiled packages are available for different distros at the sourceforge download page.

##SD4L Homepage-

##Sourceforge Page

For more disk/file encryption options under Linux