I switched to Smart Telecom and am very happy. €35 per month for 3mb broadband, free line rental, and cheaper calls.
The only problem is that the good people of eircom will do anything in their power to stop you switching. It took me three months because they kept on "forgetting" to do things like turn the dsl signal off the line, etc. Also, I had to change my number because eircom is challenging the new provider switching codes...
Smart aren't infallible, and they do go down occcasionally without notice - but then again, so did eircom...
But it is worthwhile to switch! My bill has gone from €100 per month to around €50 per month.
Other people I know are very happy with Magnet, and with NTL - so review all the options and see which one is right for you - the boards.ie Broadband board is a good source of info for this... http://www.boards.ie/vbulletin/forumdisplay.php?f=259