What version of OS X are you using? If it's recent (Snow Leopard or Lion), almost all the newest all-in-one printers (regardless of brands and models) are compatible with both Windows (XP and over) and OS X. Finding a network-operated (or shared) printer could prove more difficult, of course.
Now, buying one in an Apple Store is another matter, first because I'm not sure you can find printers there (I may be wrong, and it may depend on how big the Apple Store is; I don't remember seeing any in the Paris Apple Stores I went to, namely at the Louvres and near the Opera), and second because you're bound to pay a lot more for one in an Apple Store than in, say, a department store or an electronics retailer.
Here's a little food for thought: http://www.macbroadband.co.uk/mac-compatible/best-printers-for-apple-macs/
I've used for roughly the past year an Epson ME330 (this is the Asian marketing name—in the US it's sold under a different name). Very cheap and worked w/o problems with both the Mac and PC laptops. Comes with drivers for both, but I didn't need to install any driver for Mac OS X, either for printing or for scanning. Fine for light use, probably not suitable for a heavy workload.
If you buy a cheap inkjet, make sure to check price and availability of replacement ink cartridges.