Features of eHarmony.com:

Over 15 million registered members
10,000 - 15,000 new signups every day
Over 90 marriages a day as a result of joining eHarmony!
Split into two sections - one for singles to help you find a match, and one for married couples to help strengthen your relationship
Matchmaking site rather than dating site. You fill out a detailed questionnaire and they find matches for you. You will not have the ability to search the members' database yourself!
Compatibility Matching System - The initial questionnaire you fill in when you join will be used to find matches for you. This is an extensive 436-question questionnaire based on 29 different criteria.
eHarmony is based on the Compatibility Matching System developed by Dr. Neil Clark Warren, a relationship expert with over 35 years experience in research and private counseling (it was granted a patent in the US).
Once the system returns matches for you, you may initiate contact using a guided communication system, comprising of more questions and answers, or proceed straight to a Fast Track mode of communication.
Most subscription packages include a match guarantee.
No need to pay until a match is found for you and you wish to communicate with the other person
One of the very few dating/matchmaking sites with more female members than male
You may only search for the opposite sex. This site does not cater for same-sex relationships.
Recommended for long term, serious relationships only - not for casual dates or simple flirting!
Excellent technical support.