If you want a real light, I assume you're willing to use Li-Ion cells. With 18650 cells, there are lots of good flashlights.

I use this flashlight with this mount, and I cannot recommend the combination highly enough. The flashlight is versatile enough that you can take it off the bike and use it hand-held easily should you need to make a repair at night. It's waterproof, and has fairly "beefy" construction (not for weight weenies). That mount also lets you aim the light to the left or right by a few degrees, to see what's around the corner before you ride into it.

I've used other serious lights, like the Magic Shine, but that can't turn like the combination I just mentioned. It also does not have a self-contained battery, so you have to deal with routing its cable to wherever you decide to put its battery pack. Lastly, it's not as nice to hold as a standard flashlight, should you need to.

Edit: For rear lights, I recommend and use a Radbot 1000. While I personally can't attest to its water resistance (yet), this post claims it's quite good.