3.5 classes aren't anywhere near balanced. While this may be fine in your game, it can often be disappointing for players who are stuck at the low end of the tier list compared to the rest of the party. By making minor adjustments to the abilities of the classes, you can adjust their power levels to improve the balance of your game.
DnD 3.5 - Dungeon Master Resources
These articles pertain specifically to 3.5, but you may also find my Pathfinder Gamemaster Resources helpful because the two games are so similar.