I use Secure Form Mailer Plugin For WordPress from Dagon Design on my blogs. There are other plugins like this but I like this one, it gives me all the options I need in an easy way.
This plugin has a wide range of features including: Support for multiple instances, an easy to use dynamic form generation system (any number of fields, in any order), multiple recipients, multiple file attachments, optional auto reply feature, an image verification system, numerous security features (including protection against email header injection), a message template system, multiple languages, and too many other things to list.
This plugin was designed to be easy to use, while still being extremely flexible. If you just want a simple contact form, you can set one up with just a few clicks.
I have switched to another plugin – see WordPress Plugins I Use.