My profile from Soulgeek. I doubt this will work for a more general site.
I repeat, I suck at this. Be kind. (First thing to change: Spider Jerusalem. Even though my MOM has said I’m like him, it’s probably a bit scary)
Replace the word “geek” with “person” and you’ve pretty much stated what almost the entire population is looking for. Since the other parts of your profile are very culturally-specific, might I suggest something like:
“I’m looking for a <character that fits some personality trait you like> crossed with a <different character with another personality trait>, with a bit of <etc etc> thrown in.”
But, yanno, make it clever. And geeky.
To wit: “Sometimes I wish that Dr. Elliot Reid had visited Smallville, only to be kryptonetically merged with Chloe Sullivan, turning them both into a single neurotic, intelligent and absolutely gorgeous crime- and disease-fighting goddess. If your avatar in First Life (and maybe Second Life) happens to be just like that, then you should really email me.”
Or something like that. If you’re gonna be geeky, be GEEKY. 
I don’t fit the criteria now that I’m in a relationship, but if you had asked 6 months ago, I would have fit the bill. 
But on the upside, I can definitely say that diving into internet dating did nothing but help me. I met my girlfriend through Match.com, and it’s been absolutely awesome so far.
The biggest thing I found with online dating was that I had to keep working on making my profile better. My initial attempts were met with a resounding silence, but once I brightened up my language a bit and really tried to write about the things that I do that interest me and why, I got a lot more activity.
The biggest thing I found was to not focus on the things that were weighing on me, namely that I was lonely and didn’t really have any dating experience. Focus on the positives and the things you love, and deal with talking about the somewhat downer stuff for when you’ve actually gotten to meet someone. It’s all about presenting yourself as someone that someone else would actually WANT to be interested in. If you read your own profile from the perspective of possible dates and can’t say “Wow, she is interesting and someone I’d want to date,” Revise until you can say that. 
I re-enabled my profile on Match in case you want an example.
Something along the lines of “I’m looking for more Weird Al and less Superman”?
I think this is good advice. Keep trying different ways of wording stuff and see what gets the best response. Don’t be afraid to make jokes to SHOW the person you have a silly sense of humor instead of just telling them you do. I found that when I tried some silly humor in my own profile guys responded well to it (especially the humorous guys that were the ones I wanted).
Oh, and of course, include a flattering photo!