By pocket/keychain size I take it that you are limited to 1 x CR123. The problem is, the brighter lights have limited runtime.
For crazy bright you probably want the "TW4" combination. This is not an actual Surefire product, rather a slick combination put together by an enterprising dealer. You can build your own out of a Surefire Z57 clickie tailcap, E1e body, and KL4 head. Slap a rechargeable CR123 cell in and you have 25 minutes of insanely, crazy bright light. It's the brightest thing that sits on a keychain, period. You are essentially getting the full power of the Surefire L4 LumaMax (nominally rated at 65 lumens although some have said it "feels" more like 80). The problem is that it runs for just half an hour.
In between the wimpy 5mm LED (Sonic, CMG Inf Ultra, ArcAAA, keychain LED, etc.) and the TW4, there is my personal favorite, the Surefire E1e+KL1. Mine is an older KL1 that is dimmer, but runs for 2 hours. The newer upgraded (4th generation) KL1s run for maybe 90 minutes, but are brighter. Not as bright as the KL4, perhaps only half the power, but more than twice the runtime.
If you ask me, I'd carry a larger (two-cell) light.. my E1e+KL1 is a backup that sits on the keychain, my main light is the U2.... /ubbthreads/images/graemlins/grin.gif 150 lumens on call for all those moments where you absolutely, positively, cannot afford to compromise /ubbthreads/images/graemlins/grin.gif