Hi Carrie:

When to buy plane tickets is sort of like when to buy stock. Plane ticket prices can vary by the hour, and as I found out this year, can vary by how many are flying with you. A number of sites have notification systems that will let you know when the prices go up or down (expedia and travelocity for example).  If you find a deal on a consolidators website, go to the actual airline and check prices there. You will usually save at least $10 a ticket. Also try sites like kayak.com that search a multitude of search engines for the best price. They also search the airlines websites. Accuracy is pretty good.

July and August are the highest price times of year to travel to Europe and June is next so huge discounts aren't real likely unless you do a last minute thing and get lucky --- not the type of chance that I am usually willing to take. The downside of waiting is that last minute prices are MUCH more likely to exhorbitant, especially through Ireland.

Not sure where you live, but hubs like NY, Boston and Chicago tend to have much better fares. I was looking at prices out of Chicago (I don't live there) but prices from Chicago, stopping in Philadelphia and continuing to Dublin were cheaper (by +$200) than flights on the same airline and flight from Philly to Dublin. Airline pricing makes NO sense.

Bill