If you want to get into systems for generating new melodies, Ron Jarzombek has explained the method he used to come up with the melodic content of the songs on "The Machinations of Dementia" from his Blotted Science project (this is a
fantastic album, as essential as Petrucci's "Suspended Animation" or Barry Manilow's "Greatest Hits Vol. 3").
The Circle Of 12 Tones
Jarzombek posts video samples of each lick on the page, it's almost unbelievable without it (you'll buy the album after you watch this clip):
http://www.ronjarzombek.com/rjrem.wmv
he explains it a little more here:
The Circle Of 12 Tones
Jazz guitarist Pat Martino has a whole system based around diminished and augmented chords, rather than diatonic do-re-mi.
Click on "The Nature of Guitar", scope out pages 1 and 3 for example.
Pat Martino
I can't figure out
what the hell he's talking about, but he seems to have a good time with it.