If you do a search this topic was covered a while back.
My hubby goes to Suffolk St Surgery and is very happy with it. It's just a locum on Saturday (open till 2) but the weekday hours are quite good too. The doctors seem good and take their time with each patient.
Theres a walk in doctors surgury on Baggot st, Terenure and on Lwr Rathmines road run by the a group of a few doctors.
I've been to the one on Baggot street and they were very nice. You're seen on a first come, first seen basis and seems to be office workers in the area..
I have a business card for them - not sure of forum rules for posting phone numbers, so PM me for numbers, hours.