Simple mail contact form, the way I like it. No ajax, no bloat. No configuration necessary, but possible.
Q: What about spam?
A: Webspammers don't gain anything by spamming you through the contact form, as their links don't appear on your site. A spammer is wasting his resources by sending spammy backlinks through the form and should stop soon. Normal spam should be handled by your email provider.
Update: Since 0.6.0 there is a simple but hopefully very effective trap for automated spambots.
Q: Anybody can send me a gazillion mails through your plugin!?
A: That's true. That's why the plugin comes with a flood protection. Sender IPs are logged and an attacker would need a considerable amount of resources to bypass that protection. You can make the flood protection rules more severe if you want to.
Q: Who receives the mails?
A: The admin who activated the plugin is a registered user of your blog and has an email address associated with his account. That's where the plugin sends the mails to. This can be changed on the plugin options page.