Down in Dumbo, on Water street I think just by the Manhattan bridge overpass is Superfine. Very cool vibe and solid food.
Noodle Pudding is a great suggestion. Very recognizable italian, and very good. Cash only though!
Just, whatever you do, stay away from Grimaldi's. The pizza might be very good but it's not remotely worth the wait. (I don't know. It was very very good when I last had it 3 years ago but the lines and rudeness of the staff have kept me away since).
If you make it as far as Atlantic, I've fallen in love with Waterfalls Cafe again. Not much to look at, but the freshest, tastiest, and most caringly made Middle Eastern I've had in on Atlantic Ave.
Enjoy the walk!
if it's around 6pm you could try hecho en dumbo (on front st. in dumbo). tasty small plate mexican fare. i don't think they open before 6pm, because it's a cafe with standard coffee and paninis during the day, it just transforms to hecho at night. Noodle pudding is also a good suggestion.