e-Harmony - You've seen their ads on TV and heard them on radio. Take their Personality Profile and get instant, objective feedback on yourself and how you relate to others.

Friendfinder - With over 1,000,000 registered users, this site always has thousands of personal listings - plus chat rooms, articles and advice for Singles.

Match.com - A diverse, global community of quality single adults who share common goals - intelligent individuals who want to find great dates, make new friends, form romantic relationships or meet life partners.

Lavalife - They offer 3 distinct communities—Dating, Relationship, and Intimate. Lavalife encourages members to socialize with like-minded singles based on their individual needs and desires.

Matchmaker.com - The longest running online dating site on the web (launched in 1996). Offering a matchmaking service for a more mature audience, Matchmaker is an online dating site consisting of 35+ serious singles focused on finding long-term serious relationships and those who are marriage minded. Create your free matchmaking dating profile and find love online today.

Chemistry.com - This site is designed especially for people who are actively seeking meaningful, long-term relationships, with the belief that meaningful relationships are built on two equally important foundations: compatibility and chemistry. Other sites may help you find out if you're compatible, but Chemistry's system is designed to help you find both of these essential elements.  

Spark.com - Formerly American Singles, this site has millions of members from all walks of life, backgrounds, professions and ages, who are looking for others to share their experiences. New singles are joining all the time and tons of connections are being made every day.

PerfectMatch.com - In addition to lots of profiles and pictures, they offer a free Compatibility Profile... plus advice from relationship expert Dr. Pepper Schwartz.

2 of a Kind - They have the Net's most powerful match system featuring 150 matchable traits and interests, match analysis, anonymous email, free registration.

ChristianCafe.com - A cozy, comfortable virtual Christian Dating Service designed to enable single Christians to connect with one another in a virtual Cafe setting, from pen-pals to potential relationships.

Jewish FriendFinder - You can meet singles within the Jewish faith. Search over 90,000 Members worldwide. Anonymous email, chat, and Instant Message.

Here are some sites for Mature Singles:

LavalifePRIME - Search, chat and connect with other like-minded single Boomers, looking for everything from new relationships, networking opportunities and friends with whom to experience the adventures of life.

Senior Friendfinder - Meet Active, Single Seniors for Friendship and More. The most popular place for people over 40 looking for romance, dating and friendship.

SeniorMatch.com - They claim to be "the world's best place for meeting people over 50 for love, friendship and more." This site offers a place for 50-plus to interact with each other, talk about religion, sports, life, relationships, and more.

And here's a few sites for those NOT exactly looking for a committed relationship:

Ashley Madison Agency - ahem, how can we put it... Ashley Madison caters to men and women who may be in an unfulfilled relationship and are looking for extra marital or open spousal relationships.

Adult Friendfinder - With over twenty million active members, this is the world's largest adult site... Definitely for the more adventurous.