Ibanez Tube Screamer or the old reliable Boss DS1 - they are the easiest ones to get a nice tone with from the word go. You could get the two of those and still have change left over from $150. Or you could try and pick up a second hand Line6 DM4 Distortion Modeler. It's got pretty much every one of the big pedals modeled onto it, it's rock solid and sits on the floor like a regular stomp box with 4 different settings.