Standing out from dozens of other e-mails means having a strong subject line. You can have a longer subject, but make sure you hit the “beef” (buzzword, attention grabber, etc.) within the first 25 characters.
Think about that viewing window, too, which let’s people see the first few lines of the message before they actually click it open. Make sure you present the most important part of your message first so it’s visible in that window.
Plus, have you seen how e-mail displays on an iPhone or BlackBerry? It’s small and those great HTML photos may not even display, so make sure your copy is strong enough to stand on its own.