I have never really owned a quality flashlight, except perhaps my tiny AAA Maglight Solitaire that ate batteries and put out very little light in return. But I recently purchased a latest-gen LED flashlight that is a quantum improvement over anything I've ever used before. I'm not going to get into a lot of detail, but for the interested, there is a great flashlight FAQ here and a flashlight forum here. See also light-reviews.com and flashlightreviews.com for loads of reviews. Many lights (mostly cheap) are available on DealExtreme, and many items are listed with reviews and comments from buyers.
The flashlight revolution is all about powerful new LED emitters. We're all familiar with the little two-wire LEDs found on keychain lights or used in clusters in (cheap) larger flashlights. These are called simply "miniature LEDs." They use little power and put out decent light. But companies like Philips and Cree have developed much larger and more powerful LEDs called "power LEDs." These require heatsinks and some associated circuits to operate, but they too are very efficient and put out a lot of light.
The Cree XR-E (detailed tech) is a power LED performance/value champion and can be found in a large variety of inexpensive lights. I purchased the UltraFire C3 from DealExtreme for about $10 shipped. It is a single AA design, with an anodized aluminum body and what appears to be decent o-ring seals. It is no SureFire, but for the money I'm very happy. It puts out probably about 40-45 lumens (peak), depending on your battery. That is more than enough for any basic task and better than your typical double C-cell non-LED flashlight (e.g., 2xC Maglights produce 36 lumens). And a single, quality alkaline AA will run for about 90 min down to 50% output and will continue to put out at least some light for about twice that long. For fuller reviews, with lots of photos, see here and here.
You can find any number Cree-based AA flashlights on eBay and all over the internet. Energizer makes one that you can pick up for $17 at Target. But anything that says Cree on the box is a serious light. Upmarket, look for Fenix or the above-mentioned SureFire, the Cadillac of tactical lights. Personally, next time I will buy either the Romisen RC-G2, which is just $11.30 shipped, forward-clicky (see below), and has a little better reputation for consistent quality than my UltraFire; or spend a bit more ($16.67) on the even better MTE SSC-P4. Both are 1xAA lights.
To really get high output, you need a higher voltage light, which will typically use 2xCR123A batteries. Examples are the 170 lumen Romisen RC-E4, the 180+ lumen UltraFire C2 (review), or the fantastic 225 lumen Fenix TK10. If you prefer sticking with (cheap) AAs, there are also brighter 2xAA lights like the UltraFire WF-606A (maybe 110 lumens).
There are two things I don't like about my C3. The first is that it has a reverse click-switch, meaning that you have to click it all the way on for it to power up. A forward click-switch will allow you to depress the switch slightly for temporary light, without turning it all the way on. Also, when I first got it, mine flickered a bit until it warmed up. I just stretched the rear spring and tightened everything really tight, and that fixed it. I hope it stays fixed, but in any case, I like things to work right out of the box.
Next time I would like to get a light with a crenellated bezel (as below), which may be touted a defensive feature, but more importantly protects your lens and lets you stand your light lens-down to make a kind of mini-lantern. I'd also like another light with some real output, for effective outdoor use. There may just be an UltraFire C2 in my future.
A boutique McGizmo McLuxIII-PD: about $400, if you can even find one for sale
Addendum: See update here.