You probably already know about...
Eircom and Esat BT, who both offer ADSL (Asymmetric Digital Subscriber Line) services in Ireland. ADSL runs on a traditional phone line (not ISDN). It utilises the high end of the frequency spectrum, unused by voice, to carry data. Only certain areas of the country can be connected via ADSL at the moment, though coverage is increasing. ADSL connections start at 512 kilobits per second.

But you may not know that...
There are ways to get broadband other than ADSL.

Cable
If you are in the right area (meaning western Dublin), You may be able to get a cable broadband connection. This will give you connection speeds up to 600 kilobits per second for cheaper than current ADSL charges. go to http://www.ntl.ie for details.

Satellite
Similar speeds to ADSL or cable can be achieved via a satellite connection. This is suitable for people outside ADSL and cable catchment areas. Digiweb is an example of a company who offer this service.

Wireless
Companies such as Amocom in Cork or Leap and Irish Broadband in Dublin offer wireless internet connection systems which compete quite favourably in price with ADSL. These services are set to become much more common, especially around urban areas, in the near future.

The future
Broadband is well and truly with us in Ireland, and this list is far from exhaustive. Soon broadband will be commonplace. It's time to use it.