Yep, can recommend Nash's too - they also have a restaurant in Chapel Allerton. Another place for good fish and chips is Fish& who have a hut on Commercial Street, outside the Halifax bank. Worth a try if you are out and about.
Bretts on North Lane in Headingley is a lovely place to have a sit down fish and chip dinner, plus they are licenced so you can enjoy an alcoholic beverage with your meal. Prices are very reasonable too.