I have Eclipse (Indigo Service Release 1, Build id: 20110916-0149) running on Win XP.
I\'ve added https://dl-ssl.google.com/android/eclipse/ and installed 4 plugins
If you are going to reinstall as administrator make sure to remove the ADT Plugin from the Windows > Preferences > Install/Update > Available Software Sites.
Also something that may help is when installing the ADT Plugin you get the option for Developer Tools which the http://developer.android.com/sdk/installing/installing-adt.html guide tells you to select, but make sure to also select NDK Plugins.
And as usual do this while running as administrator. It probably doesn't make a difference but instead of clicking restart I closed Eclipse and reopened as administrator each time it was necessary.
As far as I can tell the NDK Plugin was the only thing I did differently when I finally got it to work.
I have Ubuntu , to make story short, I tried every advice here, nothing helped (reinstall, ADT removal- adding, run as sudo, deleting .eclipse folder etc). The cause of problem was running eclipse updates.
So, I downloaded ADT bundle as zip - adt-bundle-linux-x86_64-20130729 unpacked it, run eclipse inside it, used existing workplace, and it worked, 'android' option appeared in Preferences. However, there is no longer 'eclipse' splash logo at start-up, it's now called Android Developer Tools Build: v22.0.5-757759
The real solution to this issue is that you MUST run Eclipse as an Administrator before you install. There are a number of plugins that have this same issue.