if your instrument is guitar you could try some alternate tunings.. Drop D is the tuning of choice these days, but there are other conventions. For example, Kim Thayil of Soundgarden, pretty much the king of alt tunings, did an entire song with all the strings at the same pitch.. You can bang out some pretty interesting riffs by playing guitar as you normally would but with a weird tuning..
Are you familiar with the circle of fifths? Essentially, you take a piece of paper, draw a circle, stick the letter "C" at the 12:00 position of the circle and place the corresponding fifth at every hour of the clock, for example "G" at 1:00, "D" at 2:00 etc. The sequence will look like: C,G,D,A,E,B,F#,C#,G#,Eb (D#),Bb,F..
Looking at the circle, try different chords as to their relation on the "clock". Try, say, 12:00 to 6:00 to 3:00, which would give you a I,#IV,VI progression.. maybe a little dissonant for your taste, but you get the idea..
Another thing you might want to try is playing accents within a time signature to give the impression that there are multiple time signatures playing consecutively.. For example, take a 4/4 time signature and count it in eighth notes, giving you 8/8.. playing a groove in 6/8 over an 8/8 time signature will leave you with two extra beats.. (which would come out as 1-2-3-4-5-6 1-2 1-2-3-4-5-6 1-2)
I'm currently writing a song in 7/4, which is the same as 14/8.. The main riff of the song starts with a 9/8 groove with 5 beats left over, yielding a really cool 9/8 + 5/8 feel that in reality is just a 7/4 time signature!
Hope this helps,
Cy