TrueCrypt - Free Open-Source On-The-Fly Disk Encryption Software for Windows Vista/XP, Mac OS X and Linux just released version 5.0, including an OS/X version, a Linux graphical version, and lots of other goodies. Great work guys!
I installed TrueCrypt on my laptop and ran some benchmark tests.
Benchmark Results:
http://www.full-disk-encryption.net/wiki/index.php/TrueCrypt#Benchmarks
Pros:
1) Easy to use product. Simple clean interface. Amazingly user-friendly!
2) Free and Open Source
3) Multiple Encryption and Hashing algorithm available.
Cons:
1) Buffered Read and Buffered Transfer Rate were almost halved after TrueCrypt FDE was enabled :-(.
2) Access Time for large file (250+MB) increased by 11%.
3) The initial encryption of the 120 GB HDD took 2 hours.