I have almost exclusively met people for dating online, so I’d say I have a fair amount of experience in this department. I guess FB could be used for dating if you were willing to have a very open privacy level, meaning anyone can read your posts and whatnot. Otherwise, they would have a difficult time finding you or even knowing what you’re about.
Personally, you want a site like OkCupid (probably the best free dating site out there), plentyoffish.com is also free, but full of ‘not my kind of people’ (to put it diplomatically). Then, of course, you have Match.com and Chemistry. I was a charter member, in beta, of Chemistry, so I’ve had a free account there for years. It hasn’t worked out that well, though.. in all that time, I’ve only actually connected with 2 women in person. One was very nice, but not a great match. The other, not a great match, but we sure did have some awesome sexytimes there for a bit. (actually, that was seriously awesome)
One LTR (of 2½ years) came from Yahoo! Personals, but that is now defunct. I did meet and date one girl for a month off Match.