Osmos is an indie game in the vein of [flOw]. You basically have to absorb smaller motes, while avoiding being absorbed yourself by larger ones. It starts out kind of slow, but the 5th level's sheer beauty, accompanied by the ambient soundtrack make this game a joy to experience. Oh, and it also gets quite challenging.
http://www.hemispheregames.com/?page_id=17 (http://www.hemispheregames.com/?page_id=17)