When resident overseas, you may still vote in Federal elections (US President, Senate, Congress) and in some states/districts may vote for other state/local elections - contact the board of elections where you last resided to find out in which races you may vote.
If you are not registered at your overseas address, it is important to do so. For how to register abroad see:
http://www.fvap.gov/pubs/onlinefpca.html
A good resource for to help keep abreast of issues affecting US voters living overseas is the American Citizens Abroad website:
http://www.aca.ch/acan135.htm
And, it is worth noting that congress has established an advocacy group, Americans Abroad Caucus:
http://www.iht.com/articles/2007/03/...cus.php?page=1
Do please make your concerns known to your senator, representative, and to the Americans Abroad Caucus; because we are such a fractured group US expats have frequently been seen as an easy target for tax increases, etc. There are enough of us to make our views count, or at least listened to - but we have to speak up.
As my senator is running for president, I'm hoping that he'll a little more be inclined to listen this time around.
Please register, please make your views known, and please, please vote.