Ooh where do i start (I work there! )
Stock is a lovely Italian (not far from Boots) and if you are going in during the day they often have special offers at lunchtime. Simple is also lovely, but gets very busy in the evening. I have not been yet, but San Carlo is another italian that is supposed to great.
Both Zinc bar and Pizza express in the Triangle are good, and about a year ago i went to Selfridges for lunch and it was great and not too pricey (although its been rebranded to the Moet bar since so might have gone up in price). the olive press is part of the heathcotes chain and was great when we went the other week
Oh and again not tried them but two in the Northern Quarter get good reviews - Market Cafe and TNQ (next to each other not far from Shudehill bus station.
I could go on, but it really depends on what you are after and what price you want to pay. if you need any more information send me a mail
Have a nice meal
Alison