Having lived seven months in London, I can heartily endorse the following restaurants and cafes:
Mestizo. Mexican food. Just south of Camden Town. The mole brought tears of joy to our nostalgic eyes.
Sufi Restaurant (Persian) on Askew Road, south of Uxbridge Road, Shepherd's Bush. Their fresh-made bread, Persian rice and vegetarian appetizers were amazing.
Hell (pizzeria). Corner of Askew and Uxbridge, Shepherd's Bush. Reminded me of my favorite pizzeria in Austin, Texas--the Parlor, though this one is based on a pizzeria in Wellington, New Zealand. If you want great pizza, go to Hell.
Flamingo Restaurant (Ethiopian). Goldhawk Road, Shepherd's Bush. Had the vegetarian combo and it was delightful.
Punjab Restaurant on Neal near Shaftesbury Avenue, near Covent Garden. Recommended dishes: Granddad's dal (made with black lentils) and the curried pumpkin.
Cafe Blah Blah Blah. Goldhawk Road, Shepherd's Bush. Don't let the name put you off. This completely vegetarian cafe (byob) offers a wide range of delicious fare.
The Green Note, Camden Town. Great salads and appetizers, fantastic wines, and enjoyable live music.