The following is a rundown of the sites I have personal experience with. I had generally good results with this site. It is of course restricted to America Online members, so right away your pool of possibilities is cut down. I also found AOL features like Instant Messenger, Member Profile and some email features to be very helpful in getting to know someone. One drawback is that you are somewhat limited in what you post when you write an ad, in that you're really answering a set of questions.
Many people end up putting additional information in their member profiles.
I also found a problem with Love at AOL in that it seems to be down often, perhaps when they're posting new listings. The Matchmaker sites have an excellent set of features that make the experience easy and fun. Search for someone using different criteria, or browse the listings. You can view who is online and chat with them if you like. They provide your own mailbox on the site to receive mail, and allow you to see when someone has read your response, and even if they kept or deleted it.