The contact form 7 listed above is good. Or you might also use http://wordpress.org/extend/plugins/si-contact-form/ This one also has a captcha form and also uses akismet to reduce spam. I use both of them in my sites (of course only one in each site) and they are both good. I personally find the one I am mentioning in this post better for more features and find Contact Form 7 better looking. So, decide on your requirements.
I use http://www.dagondesign.com/articles/secure-form-mailer-plugin-for-wordpress/ its simple and easy to use.. try that
there are lot of plugins that are created as a contact form , but i did not find the form that fulfil all our requiremts that we need from our visitors and customers so i suggest that manually create the form and add the field as much as you require
You can do the whole process yourself: http://www.raymondselda.com/php-contact-form-with-jquery-validation/ BUT... I think is much better that you se the Contact from 7 plugin, as it will give you a workable form very fast... anyway using the link I gave you, you can add some interesting things to your form. Anyway if I want a form and I want it fast, I would go for the plugin (Make use of Wordpress!)
Just create a new page called Contact Me and use this form builder http://www.jotform.com/ and copy the code to the page
I tried many, but the best as everyone here said is Contact Form 7, and especially for me because i can change the language of the contact form other than english very easy.