You sound like a clear cut case of social anxiety. I would suggest talking to a therapist or doctor about diagnosis.
I'm similar, but different. I have no trouble finding opportunities to strike up a conversation, but even though I can think of a million things to say, I don't.
As far as conversation starters, you knows advice is good. People LOVE to talk about themselves. Ask about hobbies, or if they have a cool mp3 player or whatever tell them its cool maybe ask where they got it at, whatever. ask about their favorite things that you might be into as well. If you like movies, ask what movies they like. If there is new movie out, go see it. Then ask have you seen such and such movie yet? If they say yes then boom, you have something in common to talk about, if they so no, recommend it and tell them why its good (assuming its a good movie to begin with) this can be applied to anything - books, music, philosophy, bands, sports, TV, video games (hey have you played the new "whatever" game) current news events (hey did you hear what happened on the news today!) etc. Also, not everyone is going to like the same things you do, but there are still ways around that. You can compliment someone’s clothes, shoes, haircut, watch, jewelry, taste in music - whatever…those are all good ice breakers (even if you really don’t like their clothes shoes watch etc. Of course just breaking the ice doesn’t mean you are going to make new best friend, but it might and you never know unless you try.
In a way it may take effort. Like watching or reading current news just to strike up a conversation even if you really find the news boring. And listening is as important as talking. So don't go on and on about yourself, let the other person speak as much as you do or even more. Of course all of this is easier said then done. If you find that even with suggestions like these it is difficult, then I would suggest getting diagnosed for social anxiety...therapy and medication really can help it if that is what you have.
Just some other things that might be good ice breakers…
“hey did you study for that quiz, I hope I don’t fail” (even if you know you won’t)
“whoa, that math test was hard, how do you think you did?”
“I can’t wait to see the new will ferrel movie coming out next week, do you think it will be funny?”
“Have you heard the new “insert band name here” CD?”
I’m sure you get the idea…hope it is of some help.