I was wandering the net at random, following various links, and ended up researching a rather interesting integrated circuit that I've used before: an LM3909 LED flasher chip. It's an interesting chip which can flash a regular LED with a 2v voltage drop using only a single 1.5v battery. I used to have this breadboarded up on my bookshelf ages ago, and it would flash for months using a single AA cell, and probably for years using a D cell. The problem is that this chip is kind of hard to find these days, and when you can find them, you end up paying $5 each. What's cool is that someone actually worked out the circuit from the databook and drew up a completely discrete version.