Post your brightest rear lights here:
Mid-category:
Smart 1/2 watt flash
Relatively cheap, popular light.
Approx £12
Powered by 2 x AAA batteries, lasts a claimed 30 hours flashing, 15 steady.
Poor water resistance
Powerful category:
BLT Fantom XR9
Approx £28
Powered by 3 x AA batteries. Lasts a claimed 20hrs on full, 90 on flash.
Cheap, but limited by poor mounting brackets. This one is extremely bright, but has a relatively narrow beam.
RSP Astrum
Approx £15-20
Powered by 2 x AA batteries, lasts a claimed 8 hours on full.
Has 2 x 1/2 watt LEDs, one has a diffuser lens. It's bright, brighter than the smart 1/2 watt flash, but not as bright as the BLT Fantom XR9. It has much better side-on visibility though.
Super powerful:
Exposure Redeye
Approx £35
Lasts a claimed 9 hours on a 1 cell piggyback battery.
As bright or slightly brighter than the BLT Fantom, but over a much larger field of view. Excellent diffuser. Runs off the power port on an Exposure front light, or a stand-alone Exposure battery (1 cell piggy back battery costs £36)
Dunno much about the Dinottes or other available lights - please post if you know the gen..