Impeesa
Explorer
I'm going to ramble a bit here, but trust me, it's going somewhere.
Notice that all non-'basic' core classes (everything but fighter, wizard, cleric, rogue) can be expressed at the most basic level as a multiclass with a theme of some sort. For example, a fighter/cleric with a wilderness expert theme could be either a druid or a ranger. With a 'crusader against evil' sort of theme, he becomes a paladin. Notice that by shifting the focus between the two constituent classes (fighter and cleric) we can create two conceptually very simliar but in practice very different classes (ranger and druid).
Now, I promised this was going somewhere, and it was: Look at the bard. The bard is basically a fighter/rogue/wizard, with a 'musician' theme and no particular class focus. Now, place the primary focus on the spellcaster part, and remove the 'musician' theme. You've got a sorceror - slightly less spellcasting versatility in some respects, more in others, but with a little more fighting and social skills than a straight wizard. To balance, change the class to refllect that. One good suggestion I've seen above is up their HD to d6 - it's not like they spend a lot of time hunched over a massive book trying to wrap their mind around a spell. Since they've had more time to get out, so to speak, and their abilities are dependant entirely on charisma, give them some more social skills. Upping their skill points to 4/level may be unbalancing, but increasing their class skill selection gives them the greater potential versatility. Anyways, I suppose I've really just come down to two common house rules here, but hopefully that gives you some insight into how and why to do this.
--Impeesa--
Notice that all non-'basic' core classes (everything but fighter, wizard, cleric, rogue) can be expressed at the most basic level as a multiclass with a theme of some sort. For example, a fighter/cleric with a wilderness expert theme could be either a druid or a ranger. With a 'crusader against evil' sort of theme, he becomes a paladin. Notice that by shifting the focus between the two constituent classes (fighter and cleric) we can create two conceptually very simliar but in practice very different classes (ranger and druid).
Now, I promised this was going somewhere, and it was: Look at the bard. The bard is basically a fighter/rogue/wizard, with a 'musician' theme and no particular class focus. Now, place the primary focus on the spellcaster part, and remove the 'musician' theme. You've got a sorceror - slightly less spellcasting versatility in some respects, more in others, but with a little more fighting and social skills than a straight wizard. To balance, change the class to refllect that. One good suggestion I've seen above is up their HD to d6 - it's not like they spend a lot of time hunched over a massive book trying to wrap their mind around a spell. Since they've had more time to get out, so to speak, and their abilities are dependant entirely on charisma, give them some more social skills. Upping their skill points to 4/level may be unbalancing, but increasing their class skill selection gives them the greater potential versatility. Anyways, I suppose I've really just come down to two common house rules here, but hopefully that gives you some insight into how and why to do this.

--Impeesa--