Resources

To add / change / something in this section please go ahead to the contact & contribute section.

Websites

iPhoneDevWiki - More info on the iphonedevwiki, this is more technical.
Settings info - Documented PSSpecifiers (settings key-thingys).
SharedInstance - Has tutorials (only one at the moment).
http://developer.limneos.net/ - Has got headers for lots of iOS versions, all the way back to iOS 3.
Other random tutorials - 1, 2

Guide to create your own repo - as it says.

Communities

irc.saurik.com #theos is THE best way for direct contact with pretty much all active developers (don't quote me on this though).
/r/jailbreak is good.
/r/jailbreakdevelopers, I just saw this one 30 seconds ago, pretty small.

Files

libsubstrate_arm64.dylib

Open source tweaks

Tweakweek - Lists many open sourced small tweaks.

Headers

MP0w iOS 5 up to 7