There is the Android Market, but there are also other App stores now offering applications for the Android smartphones like Handango.
Unlike the iPhone where Apple has everything under their control, the Android eco system is a bit more open. Tetris from EA Mobile for the G1 sells for instance for $7.99.
The Google operated Android Market has about 170 apps right now. Handango offers 41 apps for the G1 right now.Explore the Android Apps available on Handango.