If you're not so sure about building one yourself, but the idea of a custom Mag floats your boat, you'll want to check out Jayrob's XM-L Maglite sales thread on CPF! Jayrob wasn't the first to modify Maglites with 10+ Watt LEDs, but he'll build you one exactly the way you want it. Jayrob has impeccable feedback because he backs up what he sells 110% and he goes over every detail with you so you'll make an informed choice. He has options for custom battery voltage monitors, superior reflectors, even a cut-down 1D stubby version--check it out!
Now, you budding flashoholic, you. I bet you're thinking, "the good old Maglite is decent: they're made in USA, tough as nails, and they are fairly inexpensive here in the States." Well, I would have to agree with you. I practically guarantee this Mag build will put a grin on your face if you've ever owned or used what is the quintessential flashlight to so many.
With a modicum of skill, resourcefulness, and patience you can modify your incandescent or LED Mag with a Cree XM-L LED, turning it into a powerhouse flashlight capable of 1000+ emitter lumens, regulated output, and multiple brightness levels. The great thing is it retains the familiar Maglite styling. A majority of high-output flashlights these days try to sell tacticool features and hyper-militant styling and simply look tacky (pocket-shredding "assault crown bezels?"). The Mag design is timeless, practical, and the body makes it a great mod host (it's a big mass of aluminum).
Below: six-thousand word essay on real-world performance
Step 1: It ain't all about flux.
Don't get hung up on losing a flux bin or two if you want a particular tint. The tint we chose for my buddy necessitated a low-ish T3 flux bin--it produces about a third less light than an XM-L U3. That might seem like a big difference, but if you want a warmer/high CRI tint, you have to accept a hit in output.
It's a game of give and take. For me, Quality > Quantity.
Update: Cree has since released the XM-L2. It's a little brighter. Generally, I recommend it if you find an XM-L2 with a desirable tint or if tint does not matter to you.