I have been playing the penatonic minor scale for about a year and it just seems i cant come up with any really killers riffs....any suggestions?
Well running over the pentatonic scale for a year is not really gonna help you write killer riffs. I would say if your main goal is to write cool riffs for songs you should just try your best to be creative and let your ears do the searching. Go note for note string a few together that sound good and speak to you and just envision what should come next.

Things like the minor scale and different arpeggio shapes can help you but you really need to think outside of the box and create something.....well creative. What is your riff gonna sound like? Is there going to be a progression of power chords behind it? Are you going to play your riff just over an Em chug? Those are the questions you should ask yourself.
Jackson DK2
1962 Fender Esquire
PEAVEY 6505+ 112