Well a lot of these haven't been mentioned yet so I thought I'd give you a list of ones I like on the subject. Lots of them have been played and replayed by everyone under the sun but good songs none the less.

Spancill Hill
City of Chicago
Missing you
Paddy's lament (Sinead O'Connor did a very good version of this in her sean nos nua album)
Skibereen
Kilkelly Ireland
Far away in Australia
The Leaving of Liverpool
Carrickfergus
Paddy Reilly
The deportee (possibly)
Nothing but the same old story

There are two or three great ones about being sent to australia as well, my favourites being 'I wish I was back home in Derry' and 'let the rope soap and calico take me'. I hesitate to add it as this one really has been overplayed to nausea inducing lengths but the fields of Athenry is a good one as well.