I have some great ideas (at least I think so), but I'm never going to get around to bringing them into reality, so I'm going throw them up here in the hope someone can capitalise on them (and assuming I can remember them) and at least I can benefit. First up: lamp timers, those things you plug into sockets, not just to switch lamps on and off, but that's what they mainly seem to be used for.
In my lounge, like many people, I have a lamp that runs off a timer. Mainly to turn on in the evening, partly for security, but also on winter mornings I have it come on so I'm not groping around in the dark. The problem is keeping it updated with when it needs to come on. In winter the light needs to come on sometimes at 5pm or earlier, while as we get to the height of summer it's more like 9 or 10pm. This is not a new, or I'm sure unique, problem.
My idea then is simple: add a light sensor. Set the time to switch the lamp on and, before it comes on, a light sensor checks the ambient light. If it's too light (this may need to be adjustable), then the lamp doesn't switch on until the light level drops. Obviously it needs some sort of override to stop it promptly switching itself off when the lamp turns on and the light level rises.
I'm not sure I've worked out all the kinks yet, for example, how does it handle plugs that are behind something? That's part of the reason for the adjustable level check, maybe an extendable sensor to get it closer to the light would work.
Ideally you want a bit more intelligence, but then you're pushing the costs right up.
For example, I'm thinking, going forward, I might try a combination of a Raspberry Pi (or my existing always-on server), with some sort of X10 or RF interface and an X10/RF lamp or socket adapter. I have no experience with any of these, but I reckon it will be possible to write a bit of code to check the time the sun sets, perhaps combine it with the weather forecast (clouds mean it'll be dark earlier than blue skies) and then knock off some time and trigger the lamp to come on, so it adapts automatically over the course of the year. If you want to get really clever you could add in some randomising factors to make it less obvious it's a timer and/or control multiple lights/devices to add that into the mix too.
You could even set it to only come on for certain months or if sun rise of sun set occur before or after certain times (to switch lamps on for dark mornings, for example).
Might be a little overkill just for some lighting, but maybe I can find a suitable device to open and close my curtains for me too (when I'm away). Home automation here we come (and don't think this sort of thing won't be standard by the end of the decade).