I personally adore this little restaurant in Covent Garden, and I have highly recommended it to many of my friends. It is close to most of the theatre's in the area, so it's great if you want something to eat before a show, or after if you're attending a matinee.
The main point is however, that the food is amazing for the price you pay. The service is of a good standard and the staff are very friendly. You can get a three course lunch for £9.90, or a three course dinner for £12.90. They serve Mediterranean cuisine, and it is just delectable.
Yes, it is a small restaurant (small being the operative word here), but who cares? There is a larger space upstairs if the downstairs area becomes over crowed. Nevertheless, I like the intimacy of the whole thing.

bistro1.co.uk
This adorable restaurant is a definite go to if you are ever in the area. There is also two other restaurants in the Soho area.
I can not recommend this place enough.
P.S. The tiramisu is to die for.