ID is not necessarily required.
e.g. in Australia, you turn up to the polling station (usually a local school or whatever), go to the desk and tell them your name. they look it up in their lists of voters, and cross your name off. Then they initial and hand you your ballot papers which you take to a private voting booth and fill out. Then you fold them and drop them into the ballot boxes (one for the house of reps, one for the senate). done.
In the last few elections, the Australian Electoral Commission (an independant govt body who have the responsibility for running elections) have been mailing out helpful voter cards with your name and IIRC your address on it which you can show at the desk. These cards are completely optional, you can still vote if you forget to bring it or have lost it or never got it, and you still don't have to show any ID.
And, yes, voting is compulsory in australia. In practice, this means you just have to turn up to a polling station and get your name crossed off the list. You can then vote informally if you choose, nobody will know. If you don't turn up, you'll get a letter in the mail a few weeks later asking if you have a good excuse (like, "I was too sick to leave the house"). If not, you'll get fined.
btw, compulsory voting is a good thing. it tends to limit the excesses of the loony extreme fringes of all sides, by encouraging politicians and major parties to pander to the middle ground.
and preferential voting (i.e. ordering your preferences as 1, 2, 3, etc) is also a good thing. it allows voters to vote for third parties and independant candidates without wasting their vote - if their first choice fails to win, their 2nd choice gets their vote...and then their third, fourth, etc choices. It also allows voters to send a message or lodge a protest, e.g. vote for the socialist party 1st and Labour 2nd - Labour will still (almost certainly) end up with that person's vote but they're also telling the Labour party that their policies are too right-wing and too cozy with business.....and, hey, if the impossible happens and the pimple-faced university student from Socialist Alliance wins a seat, that'll shake things up a bit in parliament!