Just put a lamp on a timer. I do just this during the Winter - don't really need it at the moment as enough light comes in through my bedroom windows now.
Although, the lamp I use is a 150W industrial daylight-spectrum HID, which I bought for cheap off ebay as scrap. HID lamps are very slow to warm up, and start off very dim, gradually reaching full brightness after about 5 minutes - so it works quite well as a dawn simulator (except for the fact that the light starts off green, then goes purple before finally going white). By the time the lamp has warmed up, it's so bright that it's like sitting on a beach at noon (A 150 W HID is roughly equivalent to 1000W halogen).