Sync Blocker is a brilliant app for Windows and Mac that prevents iTunes from syncing and deleting your media when iPhone, iPad, iPod, or iPod Touch is connected to the computer. It solves the biggest nightmare of an iDevice user, i.e, stops iTunes from deleting your precious media collection. Sync Blocker, which used to cost $22, is now free.
Once the application is installed, you need to request a free license which is emailed within a minute. The application consists of nothing but a single button asking you to Block iTunes Auto Sync Now, which you have to click before before plugging in your iPhone, iPad, or iPod. Once the process is complete, you can safely plug in your iDevice without worrying about iTunes deleting your media collection.
The video below demonstrates how it works.
Sadly, Sync Blocker is not portable but gets the job done. It has been tested to work with the latest version of iTunes 10.2.1.