A Google employee has published an interesting comic named Robot Evolution showing the evolution of Android OS. Until now there isn't any official statement on whether the future Android 5.0 version running on tablets and mobile phone will be named Key Lime Pie. We will have to wait until the next Google I/O which will take place on May of 2013 to find out. Of course there will be leaks before that! Anyway here is the image.
Here is a list with all the Android versions along with their codenames:
Which was your first Android version? For me it was Gingerbread 2.3.3 running on an HTC Desire.