Online daters know that moment of terror when you wonder who else is really on that site with you. Now there are answers. The new book "Click: What Millions of People Are Doing Online and Why It Matters," by Bill Tancer, shows data on the top 10 dating sites, including the male/female user ratios and the average age of visitors.

1. Singlesnet.com: 50/50 male/female; average age 45-54
2. PlentyofFish.com: 52/48 male/female; average age 45-54
3. Yahoo! Personals: 49/51 male/female; average age 35-44
4. Match.com: 44/56 male/female; average age 35-44
5. Adam4Adam: 84/16 male/female; average age 35-44
6. DateHookUp: 48/52 male/female; average age 18-24
7. eHarmony: 38/62 male/female; average age 25-34
8. ManHunt.net: 88/11 male/female; average age 35-44
9. BlackPeopleMeet: 46/53 male/female; average age 45-54
10. True.com: 42/58 male/female; average age 45-54

If you don't like those odds, you can always search somewhere more specific. Check out our unofficial list of five alternative (read: strange) online dating sites:

1. TattooedSingles.com: Share your passion for body art (even if it's washable) ...
2. SciConnect.com: Nerd alert! Find another microbe to share your Petri dish ...
3. CrazyBlindDate.com: If you prefer not to know a thing about a person (including what they look like) before you meet them face to face ...
4. ScientificMatch.com: A little DNA sample is all it takes to find your genetic match ...
5. BlueCollarDates.com: You don't have to spend your hard-earned cash at this site to find your hardworking soul mate ...