It really depends on what level of gaming you expect to do. Most of the laptops I've seen that are under 13" (Apple included) either have integrated graphics or a low-end discrete GPU (like an nVidia GeForce 8400M or 9300M).
If the laptop has a discrete GPU as an option, it usually adds $50-$100 to the price, which may push it over the top of your budget.
If you just want to occasionally play some games, but you're not trying to play Crysis on maximum settings, go with something like the Dell XPS M1330. It's an older model, but you should be able to find one with good specs (including a discrete GPU, the 8400M) for under $1k.
If you can spend a bit more, take a look at the Asus range. They've got some 14" laptops that are a little over $1k, but you can get a GeForce 130M, which should be somewhat better than the 8-9 series GeForce chips.