If you are unsure what should be the minimum required SDK for your new Android application, I suggest you take a look at the Android Developer Dashboards. It has a pie chart and table that shows you the number of Android devices that have accessed Google Play within a 14-day period.
As of this writing, you should really support Android 2.2 (Froyo) because it has 12% of the market. Going one level down to Android 2.1 (Eclair) gives you another 3.7%. There is little reason to support Android versions lower than 2.1.