For a non tactical flashlight (momentary/click button on bottom) I prefer the Underwater Kinetics [1] flashlight. These use four size AA batteries.They are widely used as firefighter helmet lights and survive well, even in fire/ground abuse environments. I try to keep everything standardized to AA and have a large stock of NiMH [2] and lithium-ion rechargeables around. For long term kit storage the comments about 9 VDC [3] lithium is right on, AA lithium batteries are also available in the camera section and can be expected to last much longer in storage than alkalines. I try to avoid CR-123 tactical and laser gear as both the rechargeable and disposable cells are quite expensive.
JWR Adds: Underwater Kinetics [1] also makes some very rugged Pelican-style hard cases.