Central

Malabar Junction is good but is purely south indian food. it is in a weird location (behind the ymca just off tottenham court rd).   I went to Malabar junction earlier this year, wasn't impressed.

I haven' t been to Chor Bizarre but have read good reviews. It may be a bit pricey.

I recently tried Benares, nice food but also expensive.

Ophim is buffet style at your table -its not that great to be honest.

I would recommend  Masala Zone. I've been several times and have never been disappointed - it is well priced. it is indian street food and as well as doing main courses etc, they do thalis that offer excellent value. the restaurant is a partnership between the owners of Veeraswamy and Chutney Marys.

Chowki is good - its the one where they have food from 3 different regions every month. Slightly small venue but good food and prices.

Rasa W1 is good but v.expensive.

I thought Mela was ok but nothing special.

Soho Spice is nice and reasonably priced

La Porté des Indes is one of the best (Gateway of Indian which is owned by the Blue Elephant group).

Outskirts
These three are good although Five Hot Chillies is more basic and does not serve alcohol :

Madhus (aka Madhu's Brilliant) in Southall (Address: 39a South Road, Southall, UB1 1SW Telephone: 02085741897) 

The Clay Oven. 13 The Mall, Ealing, London, W5 2PJ Map Telephone: 020 8840 0313

Five Hot Chillies   875 Harrow Road,Sudbury, Wembley, Middlesex, HA0 2RH - 020 8908 0666 - 020 8908 5900 (cheaper but you have to bring your own booze)

Others

Dans Le Noir - a restaurant entirely in the dark!

Tito's Peruvian Restaurant - http://www.titoseateries.com/Peruvian%20Restaurant/Peruvian_Latin_Restaurant.html