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ANY standards-compliant wireless device will work fine. Apples implementation of WiFi is usually a bit closer to fully compliant than everyone else's, but you can still use any WiFi box.
Most people say that AirPort boxes are easier to set up than other brands, but that's debatable, since there are so many other boxes that are very easy to set up. The key (and it's a shocker!) is to read the instructions that come with the product you buy. Really, it's that easy.
And before anyone else chimes in with "stay away from brand X..." let me say that I have had years of good experience with Linksys, and I've read good reports from people using D-Link, Netgear, Asante, and Buffalo products (to name a few). Shop around and get the best price, since few have any real standout features-they don't need 'em. And stay away from "Pre-N" or "speed doubler" products; the "Pre-N" products are probably going to have problems with real N-standard networks when N is finally settled next (?) year, and if you want to really double your speed with the speed doublers, you need the same brand's equipment throughout because they're not standardized.
Again, welcome!