Cool. Sounds like I'll have plenty of options for those two riffs :)

For the first one, I think it'll just come down to trying a lot of different soloing over that riff. The people I jammed with just used A Minor Pentatonic to solo over that riff, but I might like different scales to get a different sound, depending on the situation.

For the second one, it probably also comes down to playing around, depending on what key I want the song to be in. If I play it right after something in A Major, with a lengthy A Major-solo, it might be a good idea to mix between F# Minor and B Dorian, just to mix things up a little.

I've got a third one, that I came up with today. I'd like to try and figure out which scales would be good to use for this, and then if you don't mind, correct any mistakes I may have :)

Here it is:

Q Q E E Q
e|-----------------|
B|-----------------|
G|-2---------------|
D|-2---2---5-5-3---|
A|-0---3---5-5-3---|
E|-----5---3-3-1---|

Q=Quarter Note
E=Eighth Note


That's it. Now, if I were to determine which scales to use for soloing over this little riff, I'll look at the Chord/Notes used. First we have an A5 Power Chord, followed by an A Minor Chord. After this it goes down to a G5 Power Chord and an F5 Power Chord. This can imply that the Riff is in A Minor, so obviously I can use an A Minor Scale.

If we name the notes by their scale degrees in the A Minor Scale, it becomes:

e|---------------------------|
B|---------------------------|
G|-[1]-----------------------|
D|-[5]---[5]---[7]-[7]-[6]---|
A|-[1]---[m3]--[4]-[4]-[m3]--|
E|-------[1]---[7]-[7]-[6]---|


As seen, the only degree I don't use is the 2nd. This means that any scale I want to use should contain the notes A, C, D, E, F and G, which leaves me with very few options, since I'm playing in A Minor (I could be wrong on this, though). Two good options would be A Minor and A Phrygian, others might be A Pentatonic Minor or A Blues.

Am I mistaken? If so, please let me know what my mistake is, so I can learn from it :)