Ionian (major scale)- Anything major.

Dorian - ii in a major key, alternative for some minor 7 chords, minor 6 chords, minor 6/9 chords. Often used in jazz.

Phrygian - iii in a major key, alternative for minor 7th chord although dorian is probably better.

Lydian - IV in a major key, alternative for any major chord. Works well over major 7(b5) and major 7(#11) chords.

Mixolydian - V in a major key. Great scale for Dominant 7 chords.

Aeolian (natural minor) - Anything minor.

Locrian - viio in a major key. Minor 7(b5) chords.