= martyr.
So stop already. Or stop complaining. It's really very simple.
+1,000
If you're helping people with the attitude of "I'll help you, but all I ask is this one simple thing. A thank you," people will sense that you're not really doing it out of love or altruism or just being a cool guy, but that you're doing it to GET something out of the other person. No one likes a martyr. I help people all the time, but I can pretty much tell who's there to suck me dry, and who genuinely needs and will appreciate the help. And sometimes people just need help, regardless of whether they're in a position to fall all over my feet in gratitude or not. I think you need to ask yourself why you're helping others. Is it really for them, or for you to feel needed?
I was on a music-related message board and someone had offered copies of some cool high-res pics to the members there, if they'd PM an email. So I did, and thanked her graciously. A few days later, she posted a big emo message about how NO ONE had said please or thank you for these pictures, and what has this world come to, etc., etc. I reminded her that, yes I had, in fact, thanked her. And I also reminded her that if you just tell someone to PM you an email address, that's probably what people will do. You can't create unspoken rules and then get bent out of shape when people don't comply to them. If you do, you'll become very disillusioned, very quickly.
Stop and ask yourself if there might be other reasons why you're not getting the reactions you're after.