What chords are the most useful (sounds cool) to play a mixolydian scale over? With respect to modes, I realize that the mixolydian is the 5th scale of the harmonized major scale (dom 7th) but to me it sounds boring to play a mixolydian scale over a dom 7th chord (A mixolydian over A7).

I've read elsewhere that a lot of blues and rock players use the mixolydian scale/mode so where do they use it for that "hip" blues/rock sound?

Mixolydian is theoretically the "correct" scale to play over a dominant 7th chord of the same name (root). If you've given it a whirl with a variety of bends, slides, and general chicken grease, and it still sounds boring, there's a plethora of additional options available. You can add spice via chromatic, diminished, augmented, melodic minor, and harmonic minor ideas, for starters.

If you're seeking instant gratification "hipness" over a I7 or IV7 chord, you can sharp the 4/11 above the root (major scale with #4/11 and b7). This is commonly referred to as "lydian dominant" or "dominant overtone", and it can be viewed as using a melodic minor scale up a fifth from the root (that's how I initially learned it). For a V7 altered chord, you can utilize the altered dominant scale (best way for me to see it is melodic minor up a half step from the root). Some "fusion" guys utilize this sound over static dominant 7th chord vamps, although the sound personally gets on my nerves. For "inside/outside" (sweet & sour) tones, you can try playing minor7b5 arpeggios up a 3rd and a 6th from the root of the dominant seventh chord. Also try playing harmonic minor ideas up a 4th from the root.


In a Dorian situation - say, A minor (G major base tonality), D mixolydian yields some nice tones.

Check out some Jeff Beck. Maybe some live versions of "Freeway Jam". If I recall correctly, he's using G Mixolydian on that.

Steely Dans' "reelin' in the years" is a great example of mixo playing (Elliott Randall).
G to A chords - use A mixo-lydian. And, as Corleone says, "bends, slides, and chicken grease".

the mixolydian scale is the same as the major scale, just starting from a different note...

you can use G mixolydian over these chords:
C
Dm
Em
F
G
Am
Bdim

(notice these are all chords inherent in the c major scale)...