Check out Lick of the Day, a free download for iPad, iPhone and iPod touch available at the App Store http://itunes.apple.com/us/app/guitar-world-lick-of-the-day/id371728474?mt=8&at=10l5Kh&ct=gtvideo
This metal lick, inspired by Lamb of God, incorporates heavily palm-muted triplets throughout. It's pretty straightforward and stays in one position for the duration, so I'll just call your attention to a couple of things to watch out for.
Note the string-skip from the low E string to the D string going into each second beat in bars 1-3. As you catch the octave G note on the D string's fifth fret with the upstroke on beat two, be careful not to inadvertently pick any other strings. For this single-note lick to be effective, it's important to play it as cleanly as possible. Be sure to maintain a tight pick-hand palm mute, letting up on it only for the pinch harmonic (P.H.) at the end of bar 2 and for the last four chord strums.
Although the practice mode playback engine in the app plays the pinch harmonic at the end of bar 2 as D♭, I'm actually sounding an A♭. Pinch harmonics are generally used for feel anyway, so it's not all that crucial that you match the pitch. Feel free, however, to experiment with different pinch harmonic node points along the string. Most players tend to gravitate toward a consistent "sweet spot" after incorporating pinch harmonics into their playing style for some time. To get the harmonic to sound, only the very tip of the pick should be exposed so that the thumb grazes the string at the same time.
I'm using alternate picking (down-up-down-up) pretty consistently throughout, the only exceptions being downstrokes for the hits at the end of bars 2 and 4. Some of the string crosses can be a bit arduous due to the pick having to change direction in midair, so start out slowly and strive for clean execution while economizing pick-hand movement and keeping the muscles in the hand as relaxed as possible.
The tempo is 133 beats per minute, 83 for slow practice.