Logitech's Z523 Speaker system is one of four models in the company's 2009-2010 PC-speaker line that features a separate subwoofer. Though the Z523 carries a list price of $99, it sells online for $79, which makes it quite affordable--and a relatively good value.
When it released its new line in 2009, Logitech went away from the modern, squarish design of its USB-powered Z5 omnidirectional speakers and shifted to a more traditional PC speaker design. We can't say the Z523 looks or feels incredibly snazzy, but it's attractive enough, and the 4-inch subwoofer isn't imposing and is small enough to be tucked under a desk without standing out too much.
As far as dimensions and specs go, the satellites are 5.2 inches by 3.4 inches by 7.7 inches with 2-inch dome drivers on the front and the rear. The subwoofer, meanwhile, features a 4-inch down-firing subwoofer as well as a side-mounted 6.5-inch passive pressure driver. Logitech rates the system at 40 watts (it can play pretty loudly) and touts the fact that the satellites offer omnidirectional or 360-degree sound, which means you hear them even if you're standing behind them (thanks to those rear-mounted drivers).
While the rear of the speaker isn't as attractive as the front, you could have the backs facing you and still get the same sound. Like the Logitech Z320 speakers (which doesn't include a subwoofer), these guys are designed to be placed in the center of a room, though the majority of people will probably end up with the rear drivers reflecting sound off a wall since most people keep their speakers on a desk that faces a wall.