There's a nice restaurant on Leeson St. at the junction with Hatch St. called Nostromo, it's below street level although it may be more of a lunch venue than for evening meals but you can find out about them at www.nostromo.ie. Also Coopers on Leeson St. is supposed to be nice, haven't been myself though.
You could also try the Conrad hotel across the road. It's not exactly cheap, but it is very convenient (I think you can also book a space in their car park if you're spending money there).
Apart from their restaurant, you can also get food in their lounge or bar.
Another suggestion is some of the places around Merrion Row - about 10m walk. This is what I do myself (Ely Wine Bar in Ely Place).
Or there are two restaurants around the corner from Saagar on Montague Lane - Italian one the name of which escapes me (but expensive and not good service - food and wine list v. good though) or the Montague Bistro (inexpensive, reasonable food and good service)
[broken link removed] is nice, always popular with the more mature Irish as they do a lot of traditional fare, roasts, steaks, etc. Ely wine bar is also well worth checking out.
Leo
What about the Rubicon (modern European ?), Kittys Bistro (Irish / European), Bang (modern European) or the Unicorn (Italian) all on Merrion Row? - All excellent in my opinion