Renting a Flat in Dublin -- Any Thoughts?

I can't really help you with Dublin specifically but from personal experience can give you a suggestion of where to start. Do an online search for Dublin rentals; note the names and/or email addresses of any rental agents you see and start emailing them. Tell them you're looking for a short-term rental of 4-6 months, what your budget is, etc. and see what kind of responses you get.

That's exactly what I did here in the States when I was looking to move to a new city and wanted a short-term rental until I decided where in the city I wanted to settle more permanently. It took some time and legwork (online that is) but it worked.

You can try VRBO and other vacation rental sites as they do have some rentals that are willing to do longer periods like that but, since they're mostly for holiday rentals, their rates can be pretty high.

Hopefully someone here has done that, if not in Dublin then in some other European city and can give you more suggestions.

http://www.daft.ie
This is the Irish website that everyone uses that wants to rent/vacation rentals. I've used it many a times.
Do you know what part of Dublin you would like to be living in? For example Dublin 2, Dublin 6.

I have worked with HomeAway in renting a short-term flat in both Dublin and Paris. They have a large number of listings and it seems their prices are fair. Very professional group. The apartment in Dublin was on the Liffey, central, and pricey, but for 3-days it was perfect for us. Doubt that it would be reasonable for 4-6 months. I envy your length of stay!

daft.ie is the place to go. One thinkg is that it is hard to actually plan too far in advance as rentals can get snapped up very quickly when listed. You may want to consider airbnb to start with and then locate a longer term rental.

Also, be sure to verify immigration requirements as you are typically only granted 3 months (max).

Most holiday rentals in Dublin go week by week and often if your staying more the 4 or 6 weeks you get a discount.

Just in case you are not an EEA national etc, the maximum stay in Ireland as a tourist is 90 days. This applies even if you enter via the UK and get a 6 month stay in the CTA from the officer there.