Zag's approach is best. Although if your local branch is anything like the banks in Tallaght I'd ring rather than Queue. In the Past AIB have generally been the best value in FX, contrary to what you might believe if you listened to Charlie Bird.
But it's worth checking.
As for the question above about how a website is making money without charging commission, the answer is "The Spread". The difference between the price they Buy Currency for and the price they sell it for.
If they give you a little less Yen for your Euro, and when you come home they give you a little Less Euro for your Yen, they can make as much and more than someone charging commission.
Never assume that the place you bought your foreign Currency from is he best place to change it back.
Shop Around but don't kill yourself. As Zag pointed out it can be as much as €30 or €40 in €1000. That actually surprised me but it cuold well be true. But the question is how much time are you willing to spend earning a possible €40? If it's 10 or 15 minutes, I think most of us would do it.
If it's 1-2 hours queued in Banks and walking between them, I'd leave the €40 where it is.
You can also ring around, but the problem is that by the time you get down to the branch the rates might have changed. Maybe not by much, but possibly by enough to eliminate the gain of going to one bank over the other.
I don't know about all the banks, but in those that I do know about it would be very unusual for customer rates to change during the day. They are generally updated in the morning and stay the same all day.
Market rates do fluctuate all the time, but customer rates would tend to be locked in in the morning. With the involvement of IFSRA the banks obviously need to be able to go back to any date in the past and explain what rates they were using. This would be virtually impossible with fluctuating customer rates.
-Rd