I've recently been pursuing the possibility of voting in the upcoming US presidential election, since I am a US citizen. The trickiness is that I have never lived in the US but am a citizen by virtue of my parent who was born there.
The UOCAVA protects absentee voting rights of some citizens overseas, including those who have never lived there.
Here's where I've been looking; perhaps it will help you if you're also considering voting absentee.
The place I started looking was VoteFromAbroad.org, which is a legit (linked to from Obama's site) organisation designed to help overseas citizens vote.
If you're a standard citizen-by-virtue-of-a-parent, and your parent is registered to vote in a state which allows it (in my case Massachusetts, which does), you can just fill in the FPCA (Federal Post Card Application) form on that site or on FVAP.gov. On the FPCA form you fill in your vital statistics and the most recent address at which you, or the parent through whom you are eligible, were registered to vote. Then send it to the office in your local voting jurisdiction. Probably by fax at this point if you live outside the US; there's not long left!
27 days left to register! Submit your FPCA at FVAP.gov today!
— Make Your Vote Count (@FVAP) September 10, 2012
With me, it's a bit more complicated, as my American parent left the US before the first federal election they'd have been eligible to vote in, so has no registered address. However, I contacted the FVAP and asked about this, and they said (perhaps since I have a grandparent who's registered in MA):
Yes, even though they never voted, you are both eligible to vote in MA. You can fill out a Federal Post Card Application to register and request an absentee ballot from MA. When you are asked for your voting residency address, you will use your parent's last address before leaving MA.
On the FPCA form there's also an "additional information" field, so I'm hoping that if I make my situation clear then everything will go smoothly.
I've heard some concern about tax. Since I pay tax in the UK, I don't have to pay tax in the US (since I earn less than $91,500), but it's possible that I'm supposed to be filing tax returns with the IRS. I have other expat relatives who still file yearly tax returns from outside the US, though they don't have to pay any actual tax. According to VoteFromAbroad.org, just registering to vote in a federal election won't put the IRS on my case. Anyway, participating in democracy is more important than my potential inconvenience.
Update: Turns out submitting the completed FPCA form is not entirely straightforward either. In some states it must be mailed, together with a legit foreign post mark or a consul's stamp or something to prove you're actually oversees, but Mass isn't one of these. I think that Massachusetts doesn't require this. Still, I have to print (which means wrestling with this non-Euclidean horror), sign, scan and email it, and then still mail the original signed copy to Mass. Requires requests a specially printed envelope, too, so I may have to try and find a way to print directly onto an envelope...
The email address and return mail address I had to send it to were automatically generated by VoteFromAbroad.org. Mine were:
Boston Election Commissioner
Boston City Hall
One City Hall Square
Boston, Massachusetts 02201-4309
USAmaryanne DOT marrero AT cityofboston DOT gov