Let's see, in my campaign the overly-neglected skills would be: Appraise, Balance, Climb, Decipher Script, Disguise, Gather Information, Sense Motive, Speak Language, and Use Magic Device.
The most common skills on players' must-have lists: Concentration, Disable Device, Hide, Listen, Move Silently, Ride, Search, Spot, Survival, Tumble.
Skills that generally aren't worth the skill point investment, either because they're too rarely used or the DC's are usually too high to make even when skill points are invested: Forgery, Heal, Jump, Escape Artist, Swim, Use Rope.