Lord Vangarel said:
Schmoe, thanks. That's the sort of change I want to achieve. So Diplomacy and Bluff but what else uses Charisma?
Well, I don't have my books available, but Use Magic Device and Gather Information are two that jump out at me. UMD is rather specialized, but Gather Information can be very useful if your campaign involves any sort of sleuthing or just generally tracking down rumors. Also, remember that using Gather Information takes several hours (an afternoon, an evening, etc) and requires around 10gp worth of bribes (all conveniently abstracted).
I don't know how your campaign is organized, but you could try the following scenario:
Assume that the PC's have a base of operations, such as a bar, and a standard dungeon that they like to delve into to explore and gather loot. During their time at the bar, if any of them express any interest in finding out about rumors, have them make a Gather Information check. Make it so that there are a couple of easily discovered rumors (DC 12 or so) that lead the PC's toward
something to do. Then add another rumor, somewhere around DC 20, that gives the PC's clues to an easy stash of treasure.
If the PC's luck out and get the information to the easy treasure, they will be thankful that they were able to gather the appropriate information. If they don't get the rumor, have another PC group (at least equal in power to the PC's, to prevent smash'n'grab by your party) show up a week later with all of the glorious loot. Make sure that the players find out just how this other group of adventurers found the loot. Scenarios such as this will get the group thinking about Charisma and role-playing in a more positive light.
The key is that you don't want to constantly punish the players for having poor social skills, sometimes you want to reward them for having good social skills.