Markievicz Leisure centre in Townsend St. has lane and casual swimming up till 7.45pm every evening. It's quite a good pool tho can be busy. There's a rather cold sauna attached to it.
The lane swimming is good is you are an accomplished swimmer and the pool starts to get pleasantly empty after about 7.20-30pm... You'll find all the swimmers in the sauna (they're welcome to it!). The classes there run 8-9pm and the pool reopens at 9 for another 45mins (except Fridays).
I mourn the recent loss of Rathmines pool - anyone know how long it'll be closed for?
Crumlin pool's opening hours are a joke. Have yet to go out to the Tallaght Leisure complex on Fortunestown Lane, tho have heard good reports. It's only been open since 06, so should be nice & new.
Don't know of any pool open to the public in Templeogue? In my experience, membership of a type has to be bought before you can visit a private pool and most are rather small.
I know you don't want to buy membership, but a friend of mine was singing the praises of the the ESB pool on Pearse St. and if I was a better or more dedicated swimmer I might think about membership - about €350 or so per annum I think.