Character creation is done using only feats and rules from the Core rulebooks and the Complete rulebooks, with the exception of the skill tricks options presented in Complete Scoundrel. More things may be added to this list, but they will largely be here in the interest of preserving simplicity, rather than limiting options.
There is no such thing as a multiclassing penalty. If you don't know what that is, rejoice! You never have to.
The Soulknife (Expanded Psionic Handbook) class is allowed in a modified form, with all of their psionic abilities being swapped out for arcane-based ones.
The "Skill Feats" from the Player's Handbook (a series of feats that give +2 to two specific skills) now add those skills to your class list permenantly, in addition to giving the bonus.
The Ur-Priest (Complete Divine) class now only requires 5 ranks of bluff, and does not need the Spell Focus: [Evil] feat.
0th level spells are no longer expended from a character's prepared list when cast. This means you can use 0th level spells any number of times per day. A spontainous caster (such as a Sorcerer) who does not prepare spells may only use a number of different 0th level spells equal to the number they could normally cast in that day. These spells do not have to be selected ahead of time - they are simply "locked in" the first time any given 0th level spell is used that day.
The 0th level spell Cure Minor Wounds no longer cures 1 hp of damage. It still stablizes dying targets, and deals 1 damage to undead.
Spells from the Conjuration (Teleportation) school now have a minimum casting time of one round, unless otherwise specified. Teleportation spells with a casting time longer than one round already are unaffected by this change.
The portal created by Dimension Door is visible to anyone within sight of it on both ends. It omits light equal to a candle.
Teleport and Greater Teleport have a casting time of 3 rounds. The spell creates light at the other end equivelent to a candle in each square to be occupied when it is finished, starting on the 3rd round of casting. The destination cannot be changed once the casting is started.
Players may use Str or Dex for Jump; Players may use Str or Cha for Intimidate.
PCs selling items normally receive 50% of the base cost of item. However, by taking a full day to make an Appraise check, players can add 1% per point of the result check. Any number or value of items can be sold from the result of a single Appraise check. Players can take a 10 on this check, or even a 20 -- though this requires twenty days to find the right buyer(s).
Appraise now has synergies. Players receive +2 to their checks from each of these skills that have at least 5 Ranks: Bluff, Diplomacy, or Gather Information. A player with 5 ranks in a suitable Craft skill also gets +2 for matching items.
Knowledge [Local] is now a class skill for all characters. If you spent significant time in an area when you level up, you can spend 1 skill point to get two ranks in this skill (So a character who had mainly been adventuring in Melane when they leveled up could get Knowledge [Melane] for 2 ranks per skill point.)
For every rank in a Craft or Profession skill, new characters start with 5gp*level*level more starting funds. For example, a 7th-level character would normally start with 8000 gold. If they had 8 ranks in a Craft or Profession Skill, they would start with 8 * 5gp * 5 * 5 = 1,000 gp extra gold.
A number of the skills have been combined.
Disable Device and Open Lock are now Disable Device; Balance, Tumble, and Jump (dex) are now Acrobatics; Swim, Climb, and Jump (str) are now Athletics; Move Silently and Hide are now Sneak; Spot and Listen are Perception; Ride and Handle Animal are now Animal Handling; Craft now gives you a Craft AND equal ranks in a profession skill; Profession gives you any two Professions; Perform gives you any two Perform catagories. The extra Profession skill ranks granted from taking Craft or Profession don't count for increasing starting wealth. However, having multiple Craft skills stack, as do putting skill points into multiple sets of Professions.