The two most common modes apart from Ionian (major scale) and Aeolian (minor scale) seem to be Dorian and Mixolydian particularly when it comes to tunes (as opposed to songs!). The way I remember it is that Mixolydian is a major scale with a flattened seventh and Dorian is a minor scale with a sharpened sixth ie

A Dorian - ABCDEF#GA

A Mixolydian - ABC#DEF#GA

If you're working in DADGAD learn all the modes in D and buy a capo!