Happy holidays, everyone! Get it? Ghost of Christmas?
Ghosts are the third template to be assigned a LA, and the first not to be intended for summonable foddler. It's applicable to a wide range of creatures, as long as they're more charismatic than your average weasel. Obviously, the creature becomes undead. Furthermore, it turns incorporeal and can fly.
Ghosts have some hefty turn resistance, which is good as they'll be a few HD behind their party members. They get a reasonable charisma bonus, as well as a big boost to various skills. In addition, ghosts can rejuvenate after death, though the lowered HD will make reliably succeeding on the level check hard (not to mention waiting 2d4 days is kind of annoying).
Manifestation is something all ghosts have. I maintain that the ethereal-incorporeal-material rules used by ghosts are clunky and inelegant, but getting to move from the ethereal to the material plane at-will is awesome. Of note is the fact that when manifesting you still exist on the ethereal plane; there have to be ways to abuse that.
More interesting are the special abilities; ghosts can pick and choose from them, which is rare amongst templates. A few sourcebooks even present additional options!
Generally, the abilities are decent but not overpowering, though Malevolence is awesome and Chill Ray is a great combination of debuffing and damaging. Telekinesis at-will also has something going for it, of course.
I think I'll go with +3 LA for now, though I'm leaning towards +4. If one allows both the cold immunity and spell resistance suggested by Frostburn, I think +4 may be more appropriate.
Waiting for feedback!