From the latest Gartner report.

In the smartphone operating system (OS) market, Android expanded rapidly in the second quarter of 2010, overtaking Apple’s iPhone OS to become the third-most-popular OS in the world.

The rankings for the second quarter of 2010 are:

Symbian (41.2%)
RIM (18.2%)
Android (17.2%)
iOS (14.2%)
Windows Mobile (5.0%)
Linux (2.4%)
Others (1.8%)

This time last year, Symbian had 51% and Android 1.8% of the market. Apple had 13%.