I've been hunting for a good network-attached storage device for my home wireless network for several years. I've come close to buying one several times (though there haven't been many from which to choose), but always ended up deciding not to because of cost and poor integration with my Mac.
I was therefore very excited to learn about Apple's new Time Capsule. Time Capsule doubles as a wireless router and network-attached storage. Once you have it set up, it automatically backs up your hard drive using Mac OS X's Time Machine software.
By automatically, I do mean "automatically." It is the most seamless, easy to use backup system I've ever seen. At $299 (for the 500GB version) it's not cheap, but considering that you get a great a rock-solid wireless router along with a large hard drive for that price, it's definitely worth it.
Time Machine has worked with attached hard drives ever since Apple introduced it. But for a laptop family like mine, that's a bit of a waste. I work from my kitchen table, my bed, the couch, wherever. I don't want to have to lug a USB-attached hard drive with me wherever I go. Time Capsule makes this easy by backing up wirelessly using the speedy 802.11n connection.
As a bonus, swapping out my Netgear router proved a boon. I reported that with Comcast Digital Voice my router kept dropping at least once per day. No more with the Time Capsule. Its Airport Extreme underpinnings have had no problems whatsoever with my Comcast-provided cable modem/VoIP box.
The only complaint I have is that setup was surprisingly cumbersome. Most Apple products "just work." I found that whereas my Netgear routers have been super-easy to configure, the Time Capsule (and the Airport Extreme I briefly used while waiting for the Time Capsule) was not. To connect my printers wirelessly I ended up having to buy Airport Express devices to serve as printer gateways, because Apple's Airport Utility provided no clear way to add my printers and the gateways I had been using to the network. (Hours of Google searches also failed me.)
Even so, once I had it up and running, it's been beautiful. If you've got a Mac, you should get Time Capsule. You'll never lose (permanently) a file again.