Pannier Lights

Smart / Phaart lights also do a bracket that fits to the rack mounting area.

But you still need a reflector, somewhere!

I had a Cateye AU100 held on with a single screw, with slightly modified extra reflectors either side of it. But (after years of use), it's now lost the main part of the light (black back still screwed to bracket, bit with batteries and actual light missing.
I'm tempted by one of these to replace it:
http://www.bumm.de/produkte/akku-ruecklicht/toplight-flat-s.html

(I have the "Toplight Flat" (non-S, without the Linetec) on another bike, and it's okay, but not great. So I'll be interested to see other recommendations too.)

I've got a PDW Radbot 1000 light which comes with a mount that you can attach to the back of the pannier rack. They supply screws but I've found cable ties work better. Evans also sell replacement mounts so you can swap the light between multiple bikes if you want. Have been using it for a year so far with no problems.

Cateye do a mount that screws to two-hole rack reflector mounts that takes their standard rear lights.

You can use any light if you just make or buy an adaptor.