Prices: If you are from almost anywhere apart from the UK, you will find meals in restaurants to be more expensive than at home. There are some places in Edinburgh which are good and cheap, especially at lunchtime, but like anywhere else you get what you pay for. You will rarely get a good dinner with wine for less than £20 a head. Generally, prices are a bit lower than in London. Americans will find food particularly expensive, especially with the weak dollar.
If you want to eat cheaply, Indian food is the most reliable and best value. There are lots of Indian restaurants (Indian meaning from the Indian sub-continent - many of them are actually Pakistani or Bangla-Deshi).
Reservations: Edinburgh restaurants are very busy on Friday and Saturday evenings so if you're in the city for the week-end, you should always make a reservation (and don't wait until the day you want to eat). In general, we always make reservations whatever night we're eating - we've had too many disappointments in the past.
Web guides. There aren't many independent guides although there are lots of paid-for listings - the Edinburgh Restauranteurs Guide is about the most useful of these.. A generally reliable restaurant guide to Edinburgh is FineWineDiary although its far from complete. However, I don't agree with them about the Atrium where I had a disappointing and over-priced meal. The guide from the Lab for Foundations of CS is a bit out of date (several restaurants are closed) and my taste doesn't always reflect the writer's (I strongly recommend avoiding the Bombay Bicycle Club!). The local newspaper (The Scotsman) has restaurant reviews but I find their site horrible to use.