Are there any free solutions for encrypting the entire boot disk on a Mac? I'm aware of PGP's Whole Disk Encryption, but it's a bit steep at $149. TrueCrypt's System Encryption seems to only work with Windows.
The only way is as already mentioned FileVault, but FileVault only encrypts your home and swap. AFAIK there is no way to encrypt whole disk for mac.
You can try an arbitrary linux like Ubuntu or Suse, there you can choose a whole disk encryption on installation (besides /boot obviously). I have a Gentoo setup where i have my whole raid encrypted and the computer is booting from a usb key with /boot.
You should also consider if encrypting just /home with FileVault won't be enough. I mean for safely storing personal or company information it should be enough. The CIA/Russian Mafia/Taliban/Mossad will just torture you until you decrypt your harddrive :).
I would stay far away from PGP. I have used it for several years on my Windows machines and for about a year on my Mac. Recently my hard drives have started having PGP caused failures, and I have lost five in two months. PGP says this is unusual and it is unlikely to happen again, though they stated it was clearly my fault. After that conversation, while I was decrypting one of my Windows machines it failed, and the instructions from PGP were USELESS, and I couldn't save disk. I now have PGP off all my windows machines and I have taken in off my Mac. I'm using filevault on the mac and have no issues with speed, but am concerned with level of security. I am in process of encrypting windows machines with Safenet's new product. Hopefully that won't kill my machine. I have no speed issues with Filevault.