They're not the best-looking speakers in the world, but the Audioengine 2+ Premium Powered Desktop Speakers produce impressive sound. I have 'em hooked up to my 27-inch iMac.
They sport a built-in digital-to-analog converter (DAC), which provides better audio quality than the DAC built into your computer. The speaker system allows you to bypass your computer's headphone output and send music directly through USB for improved sound. You can boost the sound even more by connecting a subwoofer. You can even go wireless with Audioengine's W3 adapter (about $90).
Setup is easy. You plug the left speaker into a power outlet and connect the included speaker wire from left to right. Audioengine has included multiple inputs for connecting to your Mac or iDevice. All the cables you'll need come in the package. There’s no software to install, and A2+ works with any computer or music player.
Back to the A2+'s appearance. They're rather bland boxes that come in glossy black or white with foam padding on the bottom to prevent them (or your desk) from getting scratched. They don't take up a lot of desktop real estate (they're 6 x 4 x 5.25 inches and 3.55 pounds each) but pack a 2.75-inch Kevlar woofer, 0.75-inch silk dome tweeter, and 15-Watt amplifier into a small package. Using a similar analog design as the Audioengine 5+, the A2+ power amplifiers are built inside the left speaker, which makes for an efficient system.
Of course, it's not the appearance that counts in computer speakers, but sound. And the A2+ definitely don't sound bland. They sound good with movies (I put 'em through their paces with London Has Fallen and Killing Season) and music (used with Elton John's Wonderful Crazy Night and Alan Jackson's Bluegrass Album releases).
Even without a subwoofer connected, the bass is impressive, and the high ends, low ends and mid-tones on the A2+ are pristine and crisp. Plus, you can crank up the volume with no distortion. My only complaint is that vocals sometimes seem to lack clarity.
Overall, with the A2+ you get a solid speaker system for about US$250. And one that's expandable. For example, there are also optional speaker stands that angle the speakers a bit for an extra $29.