Seat Guru provides detailed descriptions of the seat layouts of every plane owned by major airlines. Not only does it provide a general description of cabin comfort, you can click on individual diagrams to find out the pluses and minuses of individual seats.
Airline Equality reviews airports, lounges, companies and planes, using numerical standards. In addition, the site features candid reviews of airline companies and the experiences of people who have actually flown in specific planes.
For detailed, though biased, descriptions of airline amenities, visit individual airline websites such as for Delta, JetBlue or Virgin Atlantic. Not only can you view descriptions, pictures and virtual tours of classes and services, but if you like what you see, you can book tickets on the sites.