Watch the Exotic Scales online guitar lesson by Angus Clark from Hard Rock Survival Guide: Lead
Here's the secret about the Diatonic modes. They are all based on the same sequence of half steps and whole steps that you find in the Major scale, you're just starting from a different point in the sequence. Tricky, huh? Do the math: D Major has 2 Sharps, F# and C#, if want D Lydian you raise the 4th, so now you have three sharps, F#, C#, and G# - which is also what key? A Major! If you want D Mixolydian, you lower the 7th, so now you have 1 sharp, F#, which is also what key? G Major! And so on, and so on, etc. The only difference is that the chord progression you are playing over gets you that modal sound by making D the Root.
If you want to bend minds or make an even more pronounced statement, you have to get outside the Diatonic sequence and find some other material. The Harmonic Minor scale is an example of that, and it is really well used by a guy named Yngwie Malmsteen, and if you haven't checked him out, you should watch some video of him with Alcatrazz back in the 80's. It will change you.
Richie Blackmore, Uli Roth, and Marty Friedman are all players that have used altered and exotic scales to bring new sounds into Hard Rock. If you aren't already a fan of these guys, you can hit pause on this course right now and go do some heavy listening while munching on carrot sticks or celery or whatever you prefer. I'll wait.