For natural noise: Marpac Dohm DS
While many sound machines play audio tracks on a loop, this one generates white noise mechanically with a built-in fan. The result: A natural and consistent whir. By twisting the top of the machine, you can open or close air passages until you discover the tone and volume most pleasing to your ears. Don't expect any fancy features, like an alarm clock or auto-off timer. There is only one button on this machine (the one/off switch). But the Dohm creates such realistic and calming white noise its been dubbed the official sound conditioner of the National Sleep Foundation.
For high-quality sound: Marsona DS-600A
There's a reason that Marpac, the company behind this device (as well as the Dohm), has been in the sound machine business since 1962. The Marsona isn't much to look at, and doesn't offer any special features aside from a 60-minute timer. But it's really designed to do just one thing well: help you unwind to any of six popular soundscapes—crashing surf, a babbling brook, waves lapping against a lakeshore, distant thunder, a chorus of crickets and spring peepers, and of course, white sound.
For dynamic sound: LectroFan
What makes this minimalist machine stand out is software that dynamically generates sound. Translation: No predictable looping clips! Before you go to bed, you choose one of two options—white noise or fan—and select from 10 variations in pitch and volume. For those who only have trouble falling asleep, the LectroFan provides a one-hour timer. But if you need continuous sound to stay asleep, you can run the efficient device all night long for far less energy than it takes to power an actual fan.
For super-clever tech: Ecotones Sound + Sleep Machine
The priciest of our picks, the Sound + Sleep offers a good deal of versatility. It can actually detect other noises in your environment (say, the neighbor's howling dog, or a snorer down the hall) and adjust to mask them. The gadget also has a unique "richness" feature, which allows you to add more detail to each of the 10 soundscapes (which include various nature settings, as well as options like "fireplace," "trains," and "city"). So for example, if you choose "ocean," you'll hear breaking waves. Touch the richness button to add in birds and seals. Touch it again and you'll hear bells and foghorns. Other nifty extras: A headphone jack (in case your bedmate prefers to snooze in silence) and four auto-off timer choices (30, 60, 90, and 120 minutes).
For all-night therapy: Homedics HDS-2000 Deep Sleep II
You may like zoning out to the sounds of a rainstorm—but in the wee hours, a clap of thunder may be enough to rouse you from slumber. The brilliance of this machine is that you can set it to gently transition from one of the eight water or nature settings (think "brook," "ocean," "summer night") to the steady hush of white noise after you've fallen asleep. Another bonus is the "tone" button: Turn it up for a higher pitch, or down to add bass, until you find your personal sweet spot (which the machine will remember the next time you turn it on). Want to tweak the volume, or kill the "wind chimes" and switch to "campfire"? Use the handy remote control and you don't have to leave your bed.
For portability: Homedics SoundSpa SS-2200
If you need a machine you can take on the road, this one's light (1 pound), compact (6 x 6.5 x 2 inches), and may be just what you need to relax in a strange bed. It can run on four AA batteries when, say, you're traveling abroad and short an adapter, or you've pitched your tent next to a rowdy group of Boy Scouts. Pick from six sound options: thunder, rain, ocean, summer night, brook, and your standard white noise. Plus you get an auto-off timer that you can set for as long as an hour.
For the most bang for your buck: Conair Sound Therapy
Not sold on noise machines just yet? You might want to try experimenting with this no-frills device before your spring for a more sophisticated system. For its budget-friendly price, the Conair plays an impressive 10 sound channels, including some more unusual settings like "tropical forest," "waterfall," and "heartbeat." The machine should drown out ambient noise that might be keeping you up. But if you find yourself wanting more features or better sound, you can always upgrade to a higher-end system.