Contacting professors is something you should handle carefully and fairly. Use conferences and places like that as tools and places to network with Professors.
While contacting them, do not just write emails to dozens of them all over the place and expect random replies.
Make a list of Professors and labs where you know your skills will be applicable. Make sure you keep this broad. And then contact these people. Be respectful of the fact that thousands of students similar to you will be contacting these professors. So, express patience and leave enough time between follow ups.
Make sure your emails stay to the point and do not ramble on for ever. I suggest you build a portfolio of skills on a website. And leave clear contact information. Test your emails before you send them out. Try to use text emails instead of html rich ones, since at least some of them will read them using older unix options.
Use a lot of common sense and patience.
The following would be a desirable approach when you are contacting a professor after admit and seeking funding under him.
Paragraph 1: Say who you are, where you are from and that you are admitted to the university, a professor of which you are writing to. Include evidence to that effect: student ID / registration number / application number etc.
Paragraph 2: That you don't have funding, I believe you should make it clear that you are looking for funding. So you could say, "I am looking for funding and I would be very happy to work for you." or something of that nature. Keep this very short. One, or may be two sentences.
Paragraph 3: Here's where you tell _why_ you want to work with the professor you are writing too. Talk about their projects that interest you, talk about a paper or two that they have published (preferably where they are the first author) which are of interest to you. Keep this to at most 5 sentences. Remember that to appreciate a professor's work is much more effective than flattering her.
Paragraph 4: Talk about yourself. Tell them about any of your skills, certifications etc. and how they can be of use to them. This should also be brief and cover only those aspects that you think will be of use to the professor you are writing to. The rest of it is in your resume anyway.
Paragraph 5: Close your email politely. Tell them that you have attached your updated resume and any other files (certificates etc.) and that you eagerly wait for a reply.
The bottomline: be brief. Tell them concisely, what could be of interest, and be done.