I highly recommend Aer Lingus.
They fly from Dublin to Orlando 4 times per week
I am currently in Florida and came out with them in January and paid around £250 return. I have had to change my ticket to return home and it only cost me £20, compared to the £70 that BA and many other airlines will charge you.
Each flight is priced seperately and so you aren't penalised for booking only one way.
All in all I paid £280 to get from Newcastle to Orlando, using Ryanair to get to Dublin
Hope this helps
Matt