Im a light junkie. Serfas tl 60 is a great light compatible with aero seat posts. Amazon.com has a ton of reviews. There is a performance bike axiom 60, basically identical for half the price. I have both and they are so bright, that other riders behind me ask me to angle it down or turn off. Both are 60 lumens. This is also a super light weight light, so it's a good balance between weight and brightness. You could attach the light to your helmet and seat post, for double brightness and additional angles to be seen.

Serfas makes an 80 lumen model, but it's quite a bit bulkier. I also have the Dinotte 300R- which is even brighter, brighter than a car taillight, but it's a bit bulkier, heavier, and probably too bright. Dinotte has a new, lighter weight and even brighter model than the 300R. It's more than $100, but superbly bright at 200 lumens, which is Rey bright for a red taillight.

http://store.dinottelighting.com/...in-battery-p111.aspx