I hear one thing from every single email marketing expert I talk to. No matter what marketplace you're in, there is a rule that holds true: Make your landing page (the page people click through from your email) reference your email as much as possible. The most disconnect there is between them, the lower your final conversion rate.
If your email campaign has a headline, the headline on the landing page should match it. Etc.
I was talking this over, with yet another marketer, today when I got an amazingly fabulous example of Best Practices in action in my own in-box from Old Navy. In fact it was so great, that I asked our webmistress Holly to post the email alert and the matching landing page up where you can see them here.
An additional note about this campaign (which cleverly mimics the Brady Bunch opening) is that because it mimics a TV show, it makes sense to use rich media. It's a relief to get a campaign in my in-box that uses rich media because it enhances the creative message perfectly - not just because somebody thought it would be neat-o to add. It's worth noting that Old Navy usually doesn't use rich media for campaigns. This was a conscious choice rather than a rule of thumb. I'm lost in admiration.