well to generalize, the best cases for ipod (non touch models) are the hard plastic cases you find at local retail stores. i have one several years old that still looks brand new.
the best cases for touchscreen phones (and other similar devices) is a two part system. first you will want to get yourself one of those plastic/rubberlike screen protectors they sell in retail stores and electronics shops. they might cost between $10-20 but they do save your screen. personally i use the brand at best buy with the "softer" more "rubberlike" feel to it. over time it will wear but your screen will not. you can always replace this at any time (sometimes they come in 3 packs). next you will want to get a case for the rest of the phone with an open front. typically this is a soft rubber/sillicone like substance.
if you do this your device will be protected against both minor drops and scratches. the only thing you want to watch out for is hard impacts to your screen. if you are worried about this (or are at high risk for this) then instead of a soft form fitting case get one of the hard cases (or flip open type). this is more of a hassle when you have to use the touchscreen but overall it provides the best protection against this sort of incident.