Feedburner is, hands down, the dominant RSS managment provider. Since its acqusition by Google however, few changes have been implemented on any notable scale.
That changes today as some new capabilities have been brought to the Email Branding section of FeedBurner's Email Subscriptions feature.
Users of the service are now able to display the title of the latest post in the subject line of their email to subscribers. Feedburner users posting more than one item per day and wanting to provide more descriptive subject lines will also enjoy the update, as they are able to check the "Change Subject..." box and reveal a secondary subject line to use when 2 or more feed posts are delivered in a single email.
To deploy the new feature, simply sign in to your Google Account on FeedBurner and then click your feed's title, then Publicize > Email Subscriptions > Email Branding.
Here is an image of how it will look within your Feedburner account: