Originally Posted by: rundogdaveIn the blues tune by Rush, Here Again, it opens with, I believe, a Bm, A7, E7 progression. Then in the verse it is Bm, E7, A7. I, IV, V tells me this is in the key of Em. Is this correct?[/quote]
Rush's Here Again is in the key of B minor. The E chord is the odd one with it's G# as an accidental. This gives the tune a dorian quasi blues-rock sound. But at one point they actually use a G chord if I remember correctly in climbing back to the B.

You can especially hear it is in B minor during the guitar solo. Most of what Lerxst does is in B minor pentatonic.
[QUOTE=rundogdave]And if so, is it common to start a progression on the V chord?

It is more common for classical pieces or jazz tunes to start on the V or any chord other than the tonic I chord. It is more common for rock & pop songs to start on the I. But it is not unheard of. The Beatles Oh! Darling & Chuck Berry's No Particular Place To Go both start at the "end" of their progressions with an augmented V chord (just to name 2 I can think of this early in the morning :) ).

Have fun!