Regarding rack mounts, I just picked up a Blackburn mars 2.0 because it has a screw fitting so you can bolt it directly to your rear rack.
Its a nice little light, I like the side pointing orange LEDs, though a bit annoying you need a screwdriver to change the batteries.

Also has a clip for your seatbag.

Currently running:
2x cateye ld600 on seat stays
cateye ld 100 on helmet
mars 2.0 on seatbag
reflective vest.

For touring I will ditch the ld600s and put the Mars on the rear of my rack.