I'm having mixed results with internet dating services myself, but I've finally found someone I think there's a good chance I'll get along well with.  Good luck finding that someone for yourself.
For the record, here's my thoughts on the various services I've tried:
Matchdoctor.com -- Great deal.  Free, including no spam so far (6 months+).  Pictures, criteria search, detailed essay response.  Disadvantage: very low readership.
Match.com -- Good deal.  Posting an ad, viewing ads, responding to other people's e-mail are all free; initiating a conversation requires membership / payment.  Pictures, criteria search, but short essays only, w/ no formatting.  Texans pay sales tax. 
Yahoo Personals -- Pictures, criteria, and FULL TEXT SEARCH (the only major service I've found).  Free to view or post ad, pay to respond.  Not real high traffic, at least relative to Match / Matchmaker. 
Matchmaker.com -- Most popular site, and I have no idea why.  Pictures, criteria search, detailed essays.  Pay for all functions (post, view, respond).  Still, they've got the network externality thing going; it's almost worth it just for the larger number of people who will view your ads / post their own.
EHarmony.com -- 500 question survey determines your personality type, matches you with "ideally compatible" people.  You get only a very limited number of matches, and personally, their profile was way off for me.
Brainappeal.com -- Advertised as a dating site for geeks, has pictures, and full text search, but no low traffic and no location info (!) make this less useful if you're looking for more than a pen-pal / long distance romance.
Hope this helps in finding all those people out there waiting to meet my fellow geeks. 

  Unless you're a single geek male in Houston, in which case I'll have to hunt you down an kill you in the interests of eliminating the competition. 
 
 . . . . . . . -- Eric