Hey Jill, welcome to the rabbit hole

. There's plenty of good suggestions on here about AA flashlights, so I'm gonna steer clear of recommending one, as I would just be stealing other's good ideas. Instead, let me ask:
You said AA light, but then said the tk40 looked seksy. If you're looking for single or double AA flashlights, then there is nothing (well, almost nothing) I can say except all suggestions here are great.
However, with the tk40, that's a whole new ballpark. I don't, never have, and probably never will, own a tk40. However, all the whizbang people at CPF say that 8xAA isn't a good form factor because of how complex it is- imagine christmas lights that shut off everything past a particular problem bulb. It may very well be an academic vs. real problem, I don't know. However, as the tk40 is serious money, let me share a secret with you.
The rabbit hole goes VERY deep...
I'm sick of non-rechargeable expensive batteries myself. I love surefire. The two don't really mix. However, I've found what I consider to be a terrific compromise: surefire C3, Malkoff M60w led, and some lithium ion rechargeable batteries (17500- you can get better batteries, but this is the best non-modified setup). To be fair, each battery is $11, the charger around $15, and it takes 2 batteries to run it. However, I get 170 lumens of neutral led output, for 1.5 hours, rechargeable. I carry (did, need to call warranty) a AA pocket light, and then my rocket light is the C3- one for easy universal swapping, one for power. I suppose what I need now is an HID, but I'm more interested in road bikes right now.
In conclusion: a single AA or double AA light, then there is nothing better for the job. But when it comes to extreme output, it might be worth considering going lithium. It's a little weird, I'll admit, but you can keep the form factor manageable (the TK40 is, to me, is ridiculous). Also, you don't have to keep shelling out for those expensive batteries.
Just some food for thought... or gasoline on the fire...

Zero