Here is the list of milestone to date on android OS.
20080923 - Android 1.0 [1st release]
20090309 - Android 1.1 [2nd release]
20090430 - Android 1.5 [cupcake]
20090915 - Android 1.6 [donut]
20091026 - Android 2.0 [eclair]
20100112 - Android 2.1 [flan]
20100520 - Android 2.2 [froyo]
TBA - Android 3.0 [gingerbread]




*picture courtesy of web resources*