Classes
With its easy to meet entry requirements the Charlatan Prc can be picked up by just about anyone with access to the Bluff skill. Whether a class/character should or not is really the question here.
Bard - Bards are the one core class that can enter Charlatan without purchasing cross class skills or without taking advantage of any substitution levels or alternate class features. Bard is also the only core class, aside from Sorcerer, whos primary stat is charisma. Add in some very useful social class features and spells and you've got a strong option. Glibness makes for a tempting target but that forces you to wait till eighth level minimum before getting into Charlatan and by then there are better options out there for Bards...especially since you'd be giving up caster levels...and we all know how socially acceptable that is on these boards. The spellcasting can help you get into other Prcs though...so its something to consider.
Sorcerer - Some cross class skill purchasing here but it's still Charisma based which is a plus. The spellcasting can help you get into other Prcs before or after Charlatan. The spells would also help support your lies but again you're losing caster levels so this is suboptimal.
Rogue - A tiny bit of cross class skill purchasing here as well...unless you take the changeling sub levels(and why wouldn't you?). Rogues fit the role the best of all the core classes. They're not typically charisma based, as they lean more often towards intellegence and dexterity, but it's easy enough to make a social rogue by degrading the dexterity reliance and choosing predominantly social skills. This is where the changeling sub levels from RoE shine. 10+(Int mod) skills, one free Knowledge of your choice(arcane), faster Gather Infos and Sense Motives, and taking tens on Bluff, Diplomacy, Gather Info, Intimidate, and Sense Motive. All this added on to the Changelings already stellar social abilities. The inclusion of Sneak Attack gives you some ability to defend yourself if needs be and it makes killing the noble you've cozied up to a tad bit easier as well. All in all a superb choice.
Wizard - Normally going Wizard wouldn't be too hot an idea. You're losing casting with Charlatan. That should be enough to put you off your game right there. However...the Social Proficiency Enchanter option from UA makes me, at least, sit up and take notice. And again the casting ability could help get you into another Prc.
Factotum - Without the Changeling Rogue levels Factotums make Rogues cry. Heck even with the Changeling levels Factotums can make Rogues cry. Int is your second most important stat and Factotums make heavy use of said stat. All skills as class skills means no cross class buying for you. Inspiration means your Int mod or your Factotum level to just about everything under the sun, cleric like abilities with some minor turn undead and healing, Wiz/Sorc spells as SLAs, etc. The class even provides you with a helpful cut off point just where you need it. The SLAs and the holy abilities are a real steal here as they make you more believeable. And in this case they're not your primary class feature so jumping into Charlatan isn't loosing you as much as it would with, say, Sorcerer or Wizard.
Beguiler - You're already a liar and a cheat...Charlatan just allows you to lie in new and more interesting ways. I'd take Beguiler over Sorcerer every time if I was playing a Charlatan.
Spellthief - Less optimal than a Changeling Rogue. You can borrow a few spells or SLAs from a friend to make yourself more believeable and cast a few of your own...the casting's even Charisma based...but still not as good imo.
Warlock - An interesting choice. Some cross class skill buying obviously but not much. Detect Magic at will, 10s on UMD, a Least Invocation that boosts your social skills, other Invocations that mimic spells, and a small but useful combat blast in case you get into trouble. I enjoy Warlocks despite their less than optimal status in the tier rankings. You're not even giving up as much by crossing over to Charlatan as you would if you were a normal caster. A solid choice in my book.
JesterDragComp1 - Similar to Bards in most cases. I like the class, and it fits well with the style and theme of the Charlatan, but its just not that good. It doesn't even have access to Glibness.
MountebankDragComp1 - Like a more social Warlock this has Charlatan written all over it. If it weren't for the fact that Beguiling Stare, like most of the rest of its class abilities, was based on half your Mountebank level i'd jump on this a lot more often. As it is its themeatically strong but weak design wise. Still...kinda fun.
NobleDragonlance - Another interesting choice. Charisma based, all the right skills, and abilities that are quite useful in a social setting. Not amazing but a fun choice if you like playing someone of a higher social class than the average adventurer. Basically a PC version of the NPC Aristocrat class.
Additional Prestige Classes
Mountebank(prc)CS - Adding your Int mod to your Bluff checks helps Mountebank make the list. It requires a fairly useless feat however which sours it for a lot of people. Less useful for changelings since they've already got a much more useful version of Alter Self. The Sneak Attack progression is nice, slippery mind is decent, and the tenth level ability allows you to escape if you find youself in a jam. Not an ideal Prc but appropriate for a Charlatan.
Master of MasksCS - Also useful and very appropriate for a Charlatan. The Archmage and High Priest masks are especially tempting as they offer you some SLAs to wow people with. Also offers 4/10 casting progression for any casting levels you may or may not have.
ExemplarCV - You should be able to waltz right into this Prc once you've completed Charlatan(this is assuming you entered after five levels of a base class or some such). It offers a few interesting bonuses but what you want is at first level. +4 bonus to bluff and the ability to take a ten on a small number of skills. Nice if you haven't taken the Changeling Rogue sub levels.
SpymasterCV - Not too hard to get into but many of its abilities are either copies/similar to something you've already got...only so so.
ChameleonRoD - Paydirt. A favorite of the CO community the Chameleon is an awesome choice for a Charlatan. Allows you to make your act all the more convincing. And if you get found out you can do something like this..."*sigh* No that would be my brother you're seeking. Yes he's an accomplished mage. No i'm a humble (insert class here) and I can prove it." Works best as a changeling but also excellent as a human.
Cabinet TricksterRoE - Another fun choice for a Changeling. Not as cool as a Chameleon imo but a great choice if you're going spy.
MindbenderCA - If you chose to take a starting class that had arcane casting with access to Charm Person this Prc is a fun one level dip for the 100 foot telepathy. Take it at sixth level and grab the Mindsight feat before jumping into Charlatan. If it weren't for the requirement for Arcane caster level five you might even be able to get into this class via Charlatan itself.
More to come...