• Thanks to the ubiquity of notebooks, netbooks, and MP3 players, there are plenty of options for portable, USB bus-powered speaker systems that have no need for wall warts or batteries. The majority of these speakers are relatively quiet--between 1 and 2 watts of sound--but they're all over the spectrum with regard to price, design, and functionality.
  
  

Logitech Z205 and Z305 Speakers

• The Logitech Z205 is a clip-on speaker that attaches securely to most laptops and netbooks, and it has a 1/8-inch input jack option for iPhone, iPad or other MP3 devices. It comes with a protective travel case and user documentation. The Logitech Z305 also clips onto the top of your laptop, but it's a slimmer "sound bar" with forward- and backward-firing drivers.
  
  

Altec Lansing Portable X-T2 and Orbit Speakers

• The three USB-powered speakers in Altec Lansing's Orbit series are the IML237, the slightly smaller IML227 USB Orbit Lite, and the IML237CLR. All three aluminum and composite models have an LED power indicator, a retractable stand, and storage for the 16-inch USB cord. The company's Portable X-T2 speaker has a microphone, an aux input jack for MP3 players, and an optional subwoofer output jack (it's compatible with the company's BB2001 subwoofer). It can be powered by USB for 1.5-watt performance but an AC adapter will give it a 4-watt output.
  
  

Tritton Sound Bite Speaker

• The Tritton Sound Bite is a USB-powered portable speaker that folds down to 4 inches in diameter and 2 inches thick. It has a metal grille-protected 52mm subwoofer and dual, 28mm high-end drivers. The USB 1.1 cable fits neatly in the base.
  
  

Creative Labs N400 Speaker System

• Creative Labs' compact N400 speaker system has two 2-inch drivers and an on-board control panel with volume, track, play, and pause controls. The N400, which has an input for an MP3 player, also has a headphone output. It comes with a travel case.
  
  

Coagent SP001U Music Can Speakers

• Coagent's two Music Can speakers lock together for travel but, when detached, the speakers sit at an angle and point at you. Like other USB-powered speakers, the system has storage for the 40-cm USB cable.
  
  

Hercules XPS 2.0 35 Speakers

• The Hercules XPS 2.0 speakers put out 2.5 to 3 watts of power. They're magnetically shielded so they don't disturb your surroundings. Besides a headphone jack and a master volume control knob, there's a microphone input on the front of the control speaker to make Skype or any other VoIP sessions easier.
  
  

Sony VAIO VGP-SP100 Speaker

• Sony's VAIO speakers have right and left speakers as well as a subwoofer built into one bar-shaped design. It connects with the laptop via USB 2.0. The power output is 1.2W for the right and left speakers and 1.2W for the subwoofer.
  
  

Edirol MA-1EX L/R Channel Speakers

• Edirol's pair of separate stereo speakers have 60mm drivers in a ported bass-reflex enclosure to improve its low-frequency range. They feature a headphone headset jack and S/P DIF optical output.
  
  

Lenovo ThinkVision USB Soundbar and Logitech S150 Digital Speakers

• The ThinkVision USB Soundbar is a set of speakers with 2w of output. Power and audio volume are controlled directly from the soundbar. There are two integrated headphone jacks, one on each side, for private and dual listening. The S150 Digital pair of speakers are straightforward--power on/off, volume and mute buttons, and a power LED.