Open source iOS components? Reusable views, controllers, buttons, table cells, etc?

Are there any repositories around for open sourced iPhone and iPad components?

For instance, I have found myself needing to create several new types of table cells to mimic some of Apple's existing functionality (for instance, all the different types of table cells present in the Settings application). I can't imagine I'm alone here.

Where do you go to find open sourced reusable components, or do you just write and hoard your own?

Update: I know there are open source full projects around ( see this question ), but rummaging through them and picking and choosing still leads to significant duplication of effort.

Meta: There's a site for that!

There's a new nicely browsable list of iOS controls at http://cocoacontrols.com/ .

Ongoing List

Here are some libraries that I've found or been told about (even answered here) since asking this question:

• 
  Three20 -- Custom UI classes used in the Facebook application
  


• 
  CocoaHelpers -- Extensions to common classes
  


• 
  MBProgressHUD -- Replacement for the undocumented UIProgressHUD
  


• 
  cocos2d for iPhone -- 2d game engine
  


• TouchCustoms -- Memory management, ratings, progress bars, more (GitHub Offline)
  


• 
  s7graphview -- Graphing
  


• 
  core-plot -- More graphing
  


• 
  HTFramework -- Reusable views
  


• 
  EGOTableViewPullRefresh -- Pull to refresh like Twitter (Tweetie 2)
  


• 
  PullToRefresh -- Another pull to refresh implementation
  


• 
  MGSplitViewController -- UISplitViewController replacement for the iPad
  


• 
  AQGridView -- A UITableView-style replacement that supports grids
  


• 
  DDActionHeaderView -- Combine the core concept of UIToolbar and UINavigationBar
  


• 
  DDAlertPrompt -- UIAlertView subclass providing UITextFields for user/password inputs
  


• 
  ASIHTTPRequest -- an easy to use wrapper around the CFNetwork API
  


• 
  ShareKit -- a quick way to integrate Twitter,Facebook, etc. into your app.
  


• 
  iDev Recipes - Open source code for the idevrecipes.com blog
  


• 
  QuickDialog - easy way to create dialogs, either in Obj-C or JSON
  

Source: Tips4all, CCNA FINAL EXAM