If you like Mexican food, check out Pablo Picante on Baggot Street, a "Californian Burrito Bar" serving take-away burritos. It opened earlier this year.
The food is delicious, the prices are very reasonable - mostly under €6 - and the service is fast even at peak times. This speed of service is probably due to having a simple menu. This restaurant isn't trying to do everything; it's doing just one thing and doing it very, very well.