This is the best deal on the market today. For $379 at JonesGear as of this writing (plus a 5 percent discount when you use coupon the coupon code "MacObserver"), you get 180 GH/s of mining power using about 360 watts of power at the wall. That's more hashing power running much more efficiently than the Cube. [Price updated 4/14/2014]
If the price of electricity is no object for you, you can overclock this device to 200 GH/s—overclocking increases the hashing power by roughly 10 percent, but increases the watts per gigahash of power consumption by about 25 percent.
One of the best things about this device is that it includes its own mining software—really, it's own computer—that's built right into this thing. On a Mac, Windows PC, or Linux box, you simply configure it (add your mining pool, user name, and password) from a browser and let it do its thing. Your computer doesn't have to be turned on or even connected to it once you set it up, and that makes it much more user friendly than the Cube.
It also has built-in WiFi, but you'll need to get a third-party antenna to get any range out of it. Doing so means you won't have to connect it to your network via ethernet.
If you're willing to invest US$379 (after the coupon) in mining gear, this is the way to start. It's the best price per GH/s at the entry level—roughly $2.10 per GH/s—running on the least power.
On the down side, this thing is essentially two motherboards bolted to a frame. It's open to the air, and uses a loud fan to keep it cool. if you don't admire the elegant beauty of minimalist electronics, it's unattractive and will need to be placed in a suitable place.
Tip: There are ALL kinds of cooling mods that engineers and people nerdier than me have come up with, but I found that replacing the main fan with a Corsair SP120 and adding a Scythe Gentle Typhoon on the other end of the S1 to pull air out keeps it cool with little noise.
Next: The Curious (and Cool) Gridseed Infinity