From Slashdot - "intermediate electronic voting":

General plan:
	1. Enter a booth at the polling place.
	2. Using a computer, select a candidate, or a rank.
	3. The computer outputs a card with the candidate/s along with
		barcode/s.
	4. Check that the barcodes match by looking at a sheet of paper
		put up above the computer. This sheet says "Candidate
		X's barcode looks like this".
	5. If it doesn't match, tear your card up and try again somewhere
		else.
	6. If it does, fold the card so your vote is invisible and hand to
		the election officials who put it in a box.

After the place has been closed, a machine can unfold and read all the barcodes
quickly. Upon a very narrow victory (e.g Florida), a manual count can be done
on the names on the cards. A manual count can be done on a small sample in
any case to probabilistically detect fraud as well.

We don't even need barcodes. It could be a solid slab of some color, with LEDs
and color filters to read the value.
The only place where this would be difficult is where the voters are to choose
among a huge number of candidates (think Party List interleaved STV)

More advanced systems could include encryption features like using secret
sharing to determine if your vote counted without actually revealing your vote.

[UPDATE Nov 22: Do note that this system is vulnerable to chain voting. This is
 a trick to make voting non-anonymous where the planner supplies the first 
 voter with a fake card and receives a real card that the voter smuggled
 out after giving the officials the fake card instead of the real one. The
 planner then checks that the real smuggled card is for the correct candidate
 and hands it to the second voter, perpetuating the chain.

 To prevent this, the computer should only display the card, say behind a
 glass window. A very simple and transparent mechanical system (could be as
 simple as a chute) then either dumps that card into that computer's box or
 destroys it (if the voter claims it to be false). At the end of the day, all 
 the boxes are mixed.]