I only know North London and West End really...
For Pizza and great Italian food, cheap, try La Porchetta - Stroud Green Road, Finsbury Park, this is the best one in the chain (they have 4 I think)
For a great pub meal, which includes a fantastic venue, plus great wine list, try The Lord Palmerston, Dartmouth Park Hill, Tufnell Park, they do one of the best steaks I have ever eaten.
In Camden Town, there is one of the best Japanese restaurants in london, called Bento Cafe, which is located on Parkway, No.9 - see link for details - http://www.timeout.com/london/restaurants/reviews/7518.html
If your looking for a great kebab, try the Crystal Restaurant in Holloway, Holloway, just up from the Odeon, on right hand side as if your heading towards Archway Station, one of the best Lamb Shish Kebab's around, and cheap, however venue is a bit crap to say the least.
For fish and chips, try Toff's Muswell Hill, (36 Muswell Hill Broadway) - voted best numerous times, and the restaurant is fantastic, service brilliant and food quality exceptional, however you do pay the price.
For a great Sausage & Mash, and a very good fry-up, try S & M Cafe, 4-6 Essex Road, Angel Islington, very, very good, and more importantly, cheap.
For anything italian in central london, try Little Italy - 21 Frith St, and also Italian Graffiti - 163 Wardour St, two of the best and cheapest in W1.
That's all I can think of now, but Time Out is very good, should always try that...
Hope this helps, Ciao!