Blizzard are rolling out Diablo III's Patch 1.0.4 on North American Battle.net today and in Europe tomorrow. The patch brings some welcome new features, bug fixes and balance tweaks.
The most important new feature is the Paragon system, that allows for players who have maxed out at level 60, to climb in Paragon levels. There are 100 Paragon levels, and as you increase your Paragon level core stats such as Strength, Dexterity, Intelligence, and Vitality climb in amounts similar to what you'd gain from a normal level and you also get 3% Magic Find and 3% Gold Find from each Paragon level. It may sound like a complicated way of raising the level cap, but it should bring more fun to the end game of Diablo III.
A massive amount of bugs have also been squashed and plenty of tweaks have been made to monsters and bosses.
You can find the complete patch notes over at the Battle.net forums