It would be very helpful if you gave some guidelines as to what you like, OP. There are lots of restaurants in Blackrock from McDonalds to Dali's (which got a fairly unimpressive write up in one of the national papers recently, a write up I woudn't argue with bearing in mind my one and only experience with them a few years ago. Eddie Rockets there is popular with many younger people I believe (around leaving cert generation! - that said I've no problem with a quick meal in Eddie Rockets but wouldn't go there for romance

)
The Blue Orchid (which for many years was the Japanese Ayumi Ya which I loved) is pleasant in atmosphere but I wouldn't rave about the food. There is a TGI Fridays a few yards away and an Italian in the same building as TGI's if I'm correct.
If you like Indian and are willing to travel an extra 3 to 5 minutes up the road from Blue Orchid & TGI's there is a place called Indian Summer right behind the Mill House pub which I've been to 3 or 4 times and never been disappointed, they will cook your meal cool or spicy to order.
As tara83 mentioned, have a look at menupages.ie - you can constrain searches to a particular area, see the menu of a restaurant and read some reviews of same.
As an afterthought, have a look at Monkstown just down the road from Blackrock, there are some very good restaurants there, the only ones I've been to in the last year or so were Valparaiso & Bistro Spice which were both very good in my opinion.