@Niel: That's only effective if you only have 1 fish to take out...It would be tedious to do that for a huge community tank XDDD. That is what I do though, I take my fish out and just dump the fairly stable water in.
I use a digital thermometer when taking water from the tap to match it as close as possible. I find the digital thermometers respond faster than the "analog" ones, so you can quickly and more accurately adjust the tap temperature.
I think the heated jug idea is good, but you have to watch it carefully, which I am probably too lazy to do (actually I would temporarily forget its existence).