Liner gloves are long underwear for your hands. They add significant warmth with a thin, form-fitting, next-to-skin layer. They provide full dexterity as well, making it unnecessary to strip to naked palm and fingers for things that require fine motor skills—a boon when it's frigid out. They also work well as a thin stand-alone glove in milder conditions, or as a lightweight glove when you're exercising hard in colder conditions.
Most liner gloves are made of a thin layer of polyester, which tends to rapidly shred and disintegrate with any serious outdoor use. I have an entire collection of old liner gloves with ripped fingertips and other tears inflicted from winter camping trips, ice climbing, and other cold-weather adventures. Though each pair is inexpensive ($8-$20), the costs add up if you're replacing them all the time.
The answer? Any liner glove made with Polartec's PowerStretch, which is warm, fits great due to its 4-way stretch, and is much more durable than thinner polyester liners.
I currently wear the Black Diamond Midweight Liners ($23), which to date are the only pair of liner gloves I've ever owned that have survived more than a season (they're on season two...and going strong). Black Diamond's web site is currently being updated for 2010, but you can find the glove here
I wear Black Diamond because they fit my hand the best. Other options (with different fits) include Mountain Hardwear's Powerstretch Gloves
as well as Marmot's Power Stretch Glove
. (Funny how the two manufacturers spell it differently.)
The only real drawback to liner gloves is that wind still whistles through them, which is why the Cloudveil Run Don't Walk Gloves
($40) are a great option—Powerstretch plus Windstopper Fleece in a liner glove package.