The wife and I tend to eat out much more than we should, so i've got opinions and recommendations out the yin-yang:
Bodean's BBQ
Probably one of my favorite restaurants, this chain was started by transplanted Americans and serves quality barbecue food at decent prices. The ribs and pulled pork are as good, if not better, than what I've had in the States. Lots of daily specials. Locations in SoHo, Fulham & Clapham.
http://www.bodeansbbq.com [nofollow] Joe Allen
Vaguely posh American cuisine, located in Covent Garden behind the Lyceum theater. Good eats but not cheap (probably £15-20 for entrees). Good for meals before a show, sometimes celebrities eat there, e.g. my wife has seen Damian Lewis there a few times.
Porter's
Good old British Cuisine, served without fuss. Steaks, pies, fish-n-chips, sausages, etc. Average prices. Full selection of St. Peter's brand of ales. Decor is lots of wood and green, but clean. Not full of the gaudy "antiques" that spoil a lot of places. Service is average, and the place can get busy, but since it's just a bit off the main Covent Garden square I don't know exactly how busy it gets.
Busaba Ethai
This eatery specializes in thai food. There are 2 locations, one in SoHo, and another near Tottenham Court Road station. It does not take reservations, so seating is first-come, first-served. Also they have mostly large square tables so you will almost always be put on a table with other parties. This works out OK for small parties (2 or 3) but larger groups may be waiting a while before they are seated. The place smells wonderful and is done up in nice deep dark wood finishes. I thought my curry was excellent. Prices are average for Thai food, but add-ons and drinks will make it about par with, say, a steak restaurant.
Chowki
I've always loved this Indian eatery near Piccadilly Circus. They have a rotating menu, which features three different regions of India every month. This is nice because it has more variety than other Indian places, but can be bad because if you go during the same part of the year you'll realize that you're kind of missing the point. But the food is great, and the prices are good. It's very loud, however.