A number of great alternatives have already been pointed out, but perhaps additional thought/discussion of your inital parameters would be helpful.
I suggest this because if you just became involved in LE, you really don't know what you want/need...
Is your assignment primarily vehicle-based? If so, a larger primary rechargeable light such as a Streamlight SL-20x (perhaps with sl-35 LA), SL-20XP, etc. might fit the bill.
Will you work primarily at night or day? If only during the day, a smaller duty-rig light (streamlight / surefire / pila) might be all you need.
If at night, you may want a larger primary that's rechargeable & a smaller "always on the belt" for those bail-out moments when you forget to grab the big one (or when you have to enter a dark building during the day).
Personally, I work vehicular & bike patrol, as well as footbeats ('course now it's Mardi Gras, so everthing is footbeats...)
My 'primary' light is an almost 30-year old Streamlight SL-20 (no 'x'), with an SL-35 LA & a NiMh battery stick made of 4500mAh 1/2 d's. I usually don't have to recharge this during a shift, but if I do my 'charger' is an SL-20X & its 12v adapter, also carrying another NiMh battery.
I used to carry a Surefire 6R on my duty belt, but 20 min of battery time became a problem on the bike (when the belt light became the primary), and have switched to a 9P w/the add'l throw coming in handy.
I've got a Surefire L4 in my back pocket as a backup -- also gets used when more of an 'area light' is needed, rather than a tactical light. I'll eventually purchase a Pila charger & 168s battery or two for that light as well.
When I first adopted Surefire, the 6R was great due to the rechargeable battery. As time has moved forward & 123 batteries are available for $1 each, using non-rechargeable cells has become less of an issue.
Look around your department & see what guys carry. Ask them to demonstrate their lights, so you can compare the +'s & -'s; check the boards & reviews & 'shoot-outs' here for beamshots, etc. THEN make your decision (then prepare to rethink it & buy a series of lights, looking for the perfect one! <G>)
kf