almost finished
xenocide which is the the third book and have to say the series so far has been of the rather excellent, intelligent, philosophical science fiction variety
definitely recommended, your starting poiint is the first book in the series
ender's game which is a wonderful, page turning read and you don't need to read any more books in the series after that as the first book is kind of self-contained
if you do however read more, you'll certainly be rewarded
some more info can be found
here