Tutorials

right Help Me Jailbreak is a relatively new and simple website that tells if a specific device can be jailbroken (and unlocked) or not. After answering a series of questions about a device and the user's preferences, an answer will be presented along with an updated and complete list of the currently avaliable options.

GuideMyJailbreak is another new jailbreak website that walks you through a few reasons to jailbreak, some misconceptions you may have, how to jailbreak, and how to use your new jailbroken device.

Jailbreaking
You can read lots of tutorials on iClarified. Also have a look on the ground rules concerning tutorials.
 * Jailbreak 2.2.1 (For beginners)
 * Jailbreaking 3.2.x
 * Jailbreaking 4.0 and 4.0.1

Unlocking

 * TurboSIM Unlock, for iPhone 3G

Re-Provisioning (Unlocking CDMA)

 * iPhone 4 from Verizon to other CDMA Carriers using OTA (Over The Air)
 * iPhone 4 from Verizon to other CDMA Carriers using the file system

Troubleshooting

 * Entering Recovery Mode
 * Entering DFU Mode

Semi-Technical

 * Mounting the Ramdisk of IPSW in Betas 4-7
 * Understanding iPhone Backup Files
 * Change or Customize Date and Time Formats
 * Creating a NOR-only IPSW

Reversing

 * Setting up IDA Pro Advanced to reverse the baseband

Resources
Check also the link section.