Question: RTFM is the most natural reply but I have tried that and it did not work. 

This is what I have done so far:  

1. Install all the necessary USB drivers from the vendor's site. The USB device is properly installed.  

2. Add `android:debuggable="true"` to my manifest  

3. Tried `adb devices` in command prompt and it shows the device as connected  

4. Enabled USB debugging via `Developer Settings` 

Still, my phone is **not detected in Eclipse** 

What is going wrong ? 

I am using Windows 7 32 bit and trying to connect a Samsung Galaxy S3 (GT-I9300) with the latest firmware :)

Answer: 
I have same issue with my Galaxy S3 (GT-I9300). I solved this issue after "Factory Data Reset". Now when i connect my phone with USB ,Eclipse shows my device perfectly.

Hope its helpful to you...
Download Samsung Kies mini And Than Try To Connect Your Device.