I've got another new article up for how to write riffs with intervals (two notes) instead of chord. This one shows how to do counterpoint, including parallel, contrary, and oblique motion. Lots of examples and mps!
http://www.randyellefson.com/guitar/articles/composing/interval_riff_counterpoint.html
Rock on...
Randy Ellefson
Like riffs? Melody? Shred? Free mp3s? Acoustic guitars galore? Download tunes from my new acoustic album, classical guitar album, or hard rock albums at www.randyellefson.com