A relatively new feature on WordPress.com are forms. You have been able to add a poll to a post for some time via the Polldaddy button but now you can add a form to post using the last button on the media bar (next to the polldaddy button) above the text input box:
The obvious form to create would be a contact form to collect readers details but as you can add many different sections they can be used to collect lots of different sorts of information:
This is clearly adding functionality similar to Google Forms and Survey Monkey and although it is not as functional as these other forms (e.g. no multiple choice boxes) it is a nice start and could be an excellent solution for straight forward form especially as it is so easy to add in to a blog post.