Not only do you pay excessive charges with most/all of the Irish stockbrokers but you generally don't have immediate access to buy/sell which can be an issue also.
I've had an account with Datek, now
www.TDAmeritrade.com for about 4 years now and my only outlay is a trading fee of $9.99 per transaction...no setup fees, no quarterly/annual charges and they even pay me a small percentage on my cash deposits. BTW, you don't need a bank account as they have their own account structure, just wire transfer money from your bank to theirs.
The online tools are excellent and you have full control of your own trades. Only issues that you may have is that you only trade the American exchanges and you are exposed to currency fluctuations which may increase/decrease your profits.
You are required to fill out a tax form to state that you are a non-resident and not subject to their taxes but as always are required (as a compliant tax payer) to declare your profits to the Irish taxman.
P.S. One benefit of investing in US companies is the amount of information available on the internet, some excellent message boards and reams of information. I'm currently invested in an Irish company which has traded a range for the last 12 months but am extremely frustrated because I cannot trade real-time on the cycles and also find it difficult to get timely information/opinions. The big boys are trading this I'm sure but this little guy is not getting any short term action, just relying on some long term gains.