Bitlocker equivalent for Linux

Last time I used Fedora (this was Fedora 9, YMMV), I had everything encrypted with LUKS and cryptsetup in a ext3 volume in my lvm volumes, and it did this quite well. If you want a bootable system with encrypted data hidden until a user opts to mount the right container (instead of blocking the boot process at the sake of preventing any unauthorized use like what I propose), the TrueCrypt solution mentioned above might be better. Anaconda (the Fedora installer) asked if I wanted it back then, and I tried it out of curiosity. I even hosed that laptop ages ago, and was still able to recover the data with a bootable Linux disk, so command fu, and remembering the key of course. TrueCrypt is also very well-tested, and has tons of cool features.

TrueCrypt is a free open-source alternative to Windows BitLocker. I would say that TrueCrypt is even better than BitLocker.

NOTE: This answer is out of date. TrueCrypt is no longer maintained or supported. Please consider alternative answers before using TrueCrypt.

Both Ubuntu 10.10 and Fedora 14 offer built-in disk encryption via dm-crypt/LUKS. I've used it on Fedora (to comply with my employer's mandated encryption for laptops), and found it happily painless and transparent. Basically, check the "encrypt this partition" checkbox in the installer, provide a passphrase, and there ya go.

Documentation for this feature in Fedora is at http://docs.fedoraproject.org/en-US/Fedora/14/html/Installation_Guide/encrypt-x86.html, with a lot of technical detail at http://docs.fedoraproject.org/en-US/Fedora/14/html/Installation_Guide/Disk_Encryption_Guide.html, and for Ubuntu, buried within https://help.ubuntu.com/10.10/installation-guide/amd64/module-details.html.