If you want bright, I can’t recommend the Dinotte 140 tail light enough. It’s 120 lumens which is by far the brightest I’ve ever seen (in comparison to the Cateye opticube rear light TD1000 which is 20 lumes, IIRC). Cars stay a mile off my backside now, and give me loads of respect – check out the reviews for people’s experiences.
The only downsides are that it ain’t cheap at £90, and has to be shipped from USA as no UK distributer anymore. Anyway, I figured it was way worth it – I would pay twice that for the amount of visibilty and traffic respect I get now. Absolutely awesome.