Hi Toby,
There are five or so main options in Dublin that I am familiar with or know of.
1. Flat/Apartment:
Plenty on daft.ie just now, but rents have not fallen as far as they might yet do and its real "living in the city" stuff, where in addition to the student workload you must be totally self sufficient.
In older properties there may be limited or shared facilities, the odd weirdo to dodge, possibly no broadband access and you may have to share kitchen and sanitary facilities.
In newer accommodation there may be service charges to pay in addition to the rent but the weirdos are better dressed.
In all cases there will be deposits to pay and notice to give when you're leaving.
2a. House Share
House sharing with peers is another option, where you rent a room from a main lessor and undertake to do your share of the chores and housework, and you cook and wash for yourself.
Same caveats as for flats/apartments, and you're sharing everything with people who initially at least are strangers.
Because of the closeness of the sharing, personality conflicts can arise and lead to unpleasantness.
Look at daft.ie under sharing.
Of course, the students parents could lease a house and then have some control over the situation - some, but not draconian - sharers have rights too.
2b. House Share
Several house owners appear to be offering single rooms on daft.ie [I'm not connected to daft.ie in any way], with and without en-suites [most seem to be without] as a means of making some extra income - €450-500 per month seems to be the going rate - again see daft.ie under sharing, but be careful of the ones with the photos - they may look good, but may not tell you the whole story.
3. Student Residences:
I think there's one off Donnybrook Road for girls and there are the Dartry Trinity and UCD on-Campus Student accommodation facilities.
I have no experiences of these in terms of costs or accommodation, which is reasonable by all accounts.
4. Student Hostel:
Possibly not a great long term solution
5. "Host Family" accommodation.
There are several families registered with local colleges and English Colleges in South County Dublin and elsewhere.
It is possible that the current economic downturn has left them with fewer foreign students to accommodate.
The accommodation is typically "within the family".
For young adults "student life" means no curfew and an opportunity to experiment sexually and socially and take plenty of recereational drug, drink and smoke.
Parents foresee this with some trepidation.
However, young student often undertakes to abide by a curfew, as if it were their own home and not to smoke in their room, or take drugs or have people in without the host family's permission - remember, these are strangers to the host family, not older family members whose behaviour they might otherwise assume you understand or can anticipate..
In return the student get a place to study - their room or a dining room - internet access, breakfast, a packed lunch and dinner all within a home environment.
A degree of interaction with the family is advised for foreign students, in order to practice their English and it is expected that students of all levels of ability will at least try to get on and not confine themselves to their rooms.
-----------------------------
You should always vet in person before signing up to assess the current condition of the property - and the neighbourhood, which can be a factor in terms of the relative "peace" for study, the availability of places of public resort and recreation [also necessary for study

] and the proximity to public transport.
Each type of accommodation has pros and cons; -
With house sharing you have to vet your peers, share housework and establish and budget for the contributions you will be paying towards services, utilities and communications.
Sharing a room with someone as opposed to sharing a room on a house with others can be a really poor option.
Sharing with persons who are not doing exams can be a real pain unless your headphones are really good.
With flat apartment sharing you have to vet strangers in adjoining accommodation and discover any "hidden" charges.
You may have worse problems in terms of noise during exam times than in a house share or with host family.
With any form of sharing where the occupiers do not own the house/flat/apartment you should look for evidence that the occupiers can legally sub-let to you - it would be most annoying to have to find alternative accommodation in the middle of the college year.
In general make sure the person who signs you up is the leaseholder or the landlord.
Others may have poorly defined rights under the law and make sure you keep a rent book and get signed receipts for the rent money you pay.
With family accommodation/room in a family house you have to vet your host family.
A percentage of the population are alcoholics and all families have arguments.
You will be living "under their skin" and if you have come from a sheltered home, well, let's just say that a "robust exchange" can be unsettling.
Wear protective clothing...
Yet for many parents and students a host family recommended by the school is an ideal option.
For a fixed amount all the students accommodation needs are catered for.
Its a step away from home, but yet its not completely "free flight" with all the time-consuming activities this entails.
It gives any student great support during the school year in the sense of not having to worry about budgeting, shopping for food and preparing meals, cleaning the house, clothes washing or big-brother type interaction with peers.
Yes, you get the "odd student" and you can certainly get "odd families" but in general reckon on a 5-10% "failure rate" where things don't work out.
People we know who have experienced/provided host family accommodation say they find it very rewarding.
With only one or at most two students it never becomes a business and so doesn't "take over" the family home.
They have met students from South Korea, China, Japan, Italy, France, Germany, Austria, Spain and made some good friends.
While it not particularly rewarding financially [especially now any more than one student attracts a tax liability], it certainly adds interest to the day.
This in turn has exposed them and particularly their children to other cultures, foods, languages from a very early age and that has to be a good thing.
This can be enlarged upon by some host families asking the student to help prepare one traditional meal from their country - yes including the boys - during their stay.
If this interests you, you should contact local colleges for lists of persons/families registered to provide student accommodation.
You could include places like, for example, the IADT and Anna Livia in Dun Laoghaire and secondary schools in the South Dublin.
Secondary schools sometimes run summer English courses and may also have lists of host families to draw upon.
HTH
ONQ.