Advanced Forms for WordPress Websites Just Don't Get Any Easier than Gravity Forms. Gravity Forms is hands down the best contact form plugin for WordPress powered websites.
Gravity Forms v2.0
Security enhancement: Fixed security issues in the admin pages.
Security enhancement: The location of uploaded files is now hidden by default.
Security enhancement: Added the gform_sanitize_confirmation_message filter. Return true to sanitize the entire confirmation just before rendering. This is an additional layer of security to ensure that values from merge tags used inside HTML are encoded properly and all scripts are removed. Useful for super-admins in multisite installations where site admins are not trusted.
Accessibility enhancement: Added alternative content for AJAX form iframe.
Accessibility enhancement: Added ARIA invalid and required attributes to donation, email, hidden, name, number, password, phone, post custom field, post excerpt, post tags, post title, price, select, text, textarea and website fields...