Ireland has excellent intercity and commuter transport links. What follows is a non-comprehensive list of some of those links, nationally, but with a focus on Dublin.First some websites, all have route maps, timetables etc:
Countrywide:Trains: http://www.irishrail.ie/
Buses: http://www.buseireann.ie/
(Private bus companies do also operate most popular routes).
Getting Around Dublin:
The Trams are best (called the Luas: http://www.luas.ie/). Landlords know this and tend to ask a little more near the lines. When you are deciding on where to stay, if you can get someswhere within your budget near the luas, it is a very fast and reliable service.
The Dart is a metropolitan train service (http://www.dart.ie/). Again this is reasonably reliable, although occasionally there are delays, but if you are late for work because there was a problem with the dart, so will a lot of other people, so you wont be in trouble! Again, rental prices near stations may be a little bit more expensive.
The Bus: (a very wide-ranging and comprehensive service that covers most areas): http://www.dublinbus.ie/
The Aircoach: (a coach service that connects Dublin Airport to various train stations etc): www.aircoach.ie/
Taxis: Taxi ranks are all over the city or you can hail them on the street. They are more expensive than most of the other options, but you will get there directly, and there are no taxi drivers like Dublin Taxi Drivers!
They are regulated by the carriage office: http://www.garda.ie/trafdiv/caroff.html
The Metro: (scheduled for development, more information available at: http://www.transport21.ie/)