Tutorials

JailbreakQA has jailbreaking guides, FAQs, etc. It was started by chpwn and comex, and Cydia people pay attention to it, so it's reasonably reliable and up-to-date.

GuideMyJailbreak is a 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.

http://AppletvJailbreakGuide step by step jailbreak guide.

Jailbreaking
You can read lots of tutorials on iClarified. Also have a look on the ground rules concerning tutorials.

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.