This link has lots of information on Dublin's beaches.
We live close to the beaches on the Donabate/Portrane peninsula in North County Dublin which are semi rural and, in the case of Donabate, pretty vast. The small Tower Beach at Portrane is a nice spot for a swim and the easy cliff walk from there to Donabate beach is pleasantly scenic. The beach side patio of the Waterside Hotel at Donabate is a lovely place for a drink and in good weather you could almost believe you were in the Med!
If you are using public transport take a northern commuter train from Dublin city centre to Donabate (about 25 mins). The regular 33b bus goes from there right up to Portrane beach. Donabate beach is about 2km from the railway station (it's a straight road from there to the beach). There's a taxi office in Donabate Village, just around the corner from the station and the Waterside Hotel has a free shuttle bus for customers.
If driving, exit the northbound M1 at Junction 4 and head the 4km to Donabate. Everything is well signposted from there. There's plenty of parking close to all of these beaches.
Edited: 22 May 2010, 11:56