La Porchetta, ASK, Pizza Express ,Fire & Stone in Covent Garden for Pizza
Brick Lane for curry
Chinatown is great for dim sum or try Yauatcha
Kingsland Road for Vietnamese - there are loads of places to choose from
J Sheekey in Covent Garden is a great Fish restaurant though needs booking in advance
Locanda Locatelli is fantastic Italian - needs booking in advance. For more affordable San Daniele Del Fruili in Highbury Park is good though not very easy to get to unless you are local.
Trois Garcon is a good French Restaurant - also gets you in to their cocktail bar Lounge Lover around the corner - needs booking in advance
Other good places which need advance booking Gordon Ramseys Claridges, Wolsely, Criterion, Roka
theres so many to choose from!
http://www.timeout.com/london/restaurants is a good link if you are visiting