There are no charms for ranged damage. The melee damage charm only works in melee weapons. I assume, but have not tested, that a magic damage charm would add to the magic damage done by bows or melee weapons.
I mentioned enchantments because the Increased Damage enchantment does not specify the type of damage done (other than being conventional weapon damage). If it is added to a melee weapon it does melee damage, and if added to a bow does ranged damage. The melee damage charm, however, specifically mentions melee damage/weapons in its name and description.
An Increased Magical Damage enchantment would should be the first choice for mages or intelligence based warriors, while rangers or strength based warriors should pick Increased Damage first. As a warrior/ranger I always used Increased Damage first and Increased Magical Damage second. There isn't really an obvious third choice for weapons with 3 enchantment slots; I went with Poison for my warrior and Butcher for my ranger.
