Picked up one of the new Knog Blinder lights from the shop a while ago, and so far I love it.
Tons of flash modes, to keep you endlessly entertained.
44 lumens worth of light, which is a lot for a tail light! It's designed well too. The vertical shape of the light compliments the shape of the seatpost - It LOOKS GOOD on your bike! The metal clasp is a nice touch too.
It's also USB rechargeable, so you never need to worry about batteries. Just plug it into your laptop... or wherever else you put USB plugs. Not only that, but it's pretty much waterproof. Retail is around $45. This might be the last tail light you ever buy.