The riff to this amazing song is mind-numbingly simple to play, so if you're like me and want to show off your mad guitar skillz, you can play the riff and bass line simultaneously with some judicious use of your thumbs:
E C#m G# A
E-----4-----4-----4-----4-----4-----4--0--0---0--0--
B--5-----5-----5-----5-----4-----4-----5--5p4-5--5p4
G---------------------------------------------------
D---------------------------------------------------
A--------------4--4--4--4---------------------------
E--0--0--0--0--------------4--4--4--4--5--5---5--5--
Use the thumb on your fretting hand to fret the bass notes on the E and A strings. I use a thumb pick on my other hand, and I use that to pluck the bass notes, while my index and middle fingers pick out the melody on the top strings. If you don't have a thumb pick handy, a bare thumb works in a pinch.