iPhone/Objective-C development resources

After some months developing for the iPhone I have found useful code, libraries, resources that could be useful to other developers and save time (a note, I have used only some of them):

SQLite ORMs
Persistent Objects, it allows to save and load a complex data structure in SQLite in a complete transparent way (you don't have to define even the database file name), I love it. This has a cost, the database structure is not the optimal.
ActiveRecord, I found this one complex to install for iPhone development. The approach is different, this one creates the classes that map the database, PersistentObjects creates the database that maps the objects.

HTTP Request (for RESTful APIs, POST/GET and more)
Objective-C REST Client, short library, easy to adapt to your own requirements.

JSON
JSON Framework, I used this one...
TouchJSON, ... but people seems to like more this one (I haven't try)

Inter-threading communication
ActorKit

Books
“The iPhone Developer's Cookbook: Building Applications with the iPhone SDK” by Erica Sadun, I think this one was the first one and, in any case, is the one I have. For me a good book and the source code is available here, besides that she has set up a google group iPhoneSDK with lot of activity.

Other books are appearing, for instance, this one for beginners “Beginning iPhone Development: Exploring the iPhone SDK” , in iPhone development, not in Objective-C (it has a lot of success, I can’t talk about the quality I don’t know).

Google Groups
I have found two groups with significant activity:
iPhoneSDK , mentioned previously, and
iPhone SDK Development

Curiosities
Today I have found this Google docs spreadsheet with twitter URLs of iPhone developers. (mine for SmartTime is included ;) )
You can include new ones in this form.

That’s all.
Comments? Something missed?

--edu