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).