C4 Streamlight PolyStinger and Surefire E2DL:
I carry two lights on duty: a 185 lumen C4 Polystinger, and a 200 lumen Surefire E2DL. Bought them both at Gulf State Distributors which is the biggest duty store in Alabama, and they really aggressively price stuff for LEO's. I paid around $120 of the Polystinger, and $118 for the E2DL. I also bought the fast-charger for the Polystinger.
For heavy rain and illuminating car interiors I recommend the Surefire E2DL. Not only is it 200 lumens, it has a fuller (wider) beam pattern without being too wide. The wider pattern is also better in buildings as the polystinger's pattern is just a bit too tight. Of course the Surefire has spoiled me, I thought the Polystinger was just amazing until someone loaned me a 200 lumen Surefire.
Someone on this thread recommended the LX2. I would not recommend the LX2 if you do traffic stops because of the user interface. I have both the E2DL and the LX2 (After one shift with the LX2 I definitely ended up liking the E2DL because of the excessive pressure it takes to keep the LX2 on high - if your thumb lets up even ever so slightly the LX2 drops down to 25 lumens until you're squeezing the crap out of it again to get it back up to 200 - hardly practical during a traffic stop. You shouldn't be paying that much attention to your light in a safety situation, tactical or otherwise).
With the E2DL you click it once for high beam and you're at 200 lumens until you click it again, and it really illuminates the interior of a vehicle on stops. Some will point out that besides the momentary button in the rear, the LX2 also stays on by twisting the back - but this is very impractical for LE because the throw of the twist is WAY too long, almost 340 degrees of twisting to get from low to high beam making it a dangerous two-handed process or tricky and lengthy one-handed process in which the clip still gets in the way in either one. Just a quick click with the E2DL, and the E2DL is a decent little weapon, and Safariland makes a duty-belt holster for the E2DL.
For the bigger light, if I didn't have the Polystinger I would carry a Pelican 7060. I have a Pelican 8060 in the car that is a great big back up, I thought I would use it at vehicle checkpoints or working races, but really haven't.