As just a random idea for buffing skills, is just an "Intuitive Skill" system.
You may select a 2 + Cha skills (Unless you have 6 or more skill ranks, then it's just Cha mod), linked to a class skill you possess. You gain skill ranks in those skill equal to 3/4ths your character level. This increases automatically as you level.
Basically, to serve to make Charisma kinda useful, and improve other classes skill ranks.
Maybe make this a feat?
Intuitive Skills
Prerequisite: Cha 14+
Benefit: You gain two additional skill points per level that can only be spent on ranks in Cha based skills.
Not exactly on topic, but I liked someone's suggestion (Deadmanwalking I think) that a character can choose to have will saves based on either wisdom or charisma.
Charisma skills have the problem that they are generally mutually exclusive. You won't be bluffing at the same time as using diplomacy at the same time as using intimidate, and indeed one of those three will probably get you through most situations you would use any of the three in (meaning charisma is really only helping you with 2 skills: one of the above, and UMD)
Could be "things you picked up because people like to talk to you". That could be skills like you suggested, or it could be you can use Cha for untrained skill checks, instead of the appropriate skill. Applies to Knowledge skills, but DC is increased by 5 (since they are trained only).