So here's a simple tutorial I made on how to farm blazes and kill them in 1-shot kills. There's bound to be better methods, but I'm putting mine out there. I hope it is useful to at least some people, so enjoy!
so you push them off the edge ... but if you put wallsigns below the edge wound't they walk alone off it?
Well, the sign trick doesn't work anymore as of 1.0. It was broken. Also, if you just let them walk off the edge, then you will get lower spawn rates, because the wondering blaze might not be out of range of the spawner. If some are in range, then it slows down the spawner's potential.