Salads are a very difficult food to pair wines with... or at least that's what I hear. My general rule of thumb is, when in doubt, choose a bubbly! These wines can go with practically any food. The acidity is crisp enough to eat through anything, the natural carbonation of sparkling wine refreshes the palate, and the wine flavors are subtle enough that it won't overpower (or under power) your salad of choice.
The other good option are light, acidic, un-oaked white wines (think Riesling, Gewurztraminer, Rkatsiteli, un-oaked/naked Chardonnay, Pinot Grigio, Gruner Veltliner, Sauvignon Blanc, Chenin Blanc, etc.). These wines don't accentuate the astringency from a vinegar-based salad dressing.
One suggestion I've read (thank you Wine Diva) is to change your lettuce base. Apparently greens like endive, radicchio, arugula, watercress, Boston, and red oak are milder in their flavor, or lack excessive amounts of chlorophyll that interfere with the wine flavors. So mixing lettuce types could be a big bonus for your salads.
For those red wine lovers, stay away from heavy reds (aka Cabs, Bordeaux blends). Instead try pure Sangiovese, Pinot Noir, light Merlots, Gamay or Mouvedre. Typically these varieties are made in styles that do not use heavy oaking, and have enough acidity to match that of the salad.
Another useful Wine Diva tip is if you are making your own salad dressing, instead of using a vinaigrette, make a wine reduction base (heated olive oil that slowly has your wine of choice added to it... with whatever spices you may want to include). After allowing the reduction to cool, you can use it as the dressing on your salad. This is a great idea because it will match the wine your serving. Easy-peasy!
(All photos from Google Images)
Remember to ultimately drink what you like. And again, if you ever feel under pressure - sparkling wine is the answer! Cheers!