So far my favorite (price aside) toy that seems to have the right features to make you a better hypermiler and some useful non glitzy extras is the dynodash
Screen Shots - Scan Tool, Performance Meter, Data Logger | DashDyno SPD
But it is an incremental tool over the scangauge or the mpguino for that matter in terms of the essential feedback items. You can make a whole lot of improvement with just an instant mpg and a trip mpg.