This question is too broad. What do we mean when we say "balanced" or "unbalanced." Don't get me wrong, the question is straight-foward, but in terms of what?
- PVP?
- Straight Dungeon-Crawling
- Roleplay?
- Hack n Slash through the Monster Manual?
- Magic-User vs Non-Magic User?
- Item-Dependence vs. Natural Ability?
- High Magic games vs. Low Magic Games
There are just too many variables, and as another poster mentioned earlier, half of the "balancing" action that occurs in a game is up to the DM. I could make a campaign where monks rule the day and wizards can't find a single spell to add to their spell-book. That wouldn't mean that wizards were underpowered in the slightest, just that my campaign was tailored against them. Likewise, I could make a campaign where the monk runs into nothing but non-humanoid, gigantic rock creatures with high AC and DR/Silver. Nothing in the monk's aresenal is going to really help in that situation, even if he finds a silver kama to wield. But then watch the party wizard come up with a thousand different ways to nuke these rock creatures, or even possess them and create a diabolical army of rocks.
The characters, as is, are fairly close to each other. Go to the wizards board for powergaming and you'll find threads that usually point to the druid, not the cleric, as the most powerful class, but that's based on number crunching alone. It doesn't take into account any roleplaying, any themes in the campaign, or even item placement. It's based on opening up the book, turning to your favorite page, and equipping yourself with whatever you want, so long as the DM gives you the GP to buy it. Of course you're going to find some unbalanced features.