WordPress 2.5, the culmination of six months of work by the WordPress community, people just like you. The improvements in 2.5 are numerous, and almost entirely a result of your feedback: multi-file uploading, one-click plugin upgrades, built-in galleries, customizable dashboard, salted passwords and cookie encryption, media library, a WYSIWYG that doesn’t mess with your code, concurrent post editing protection, full-screen writing, and search that covers posts and pages.
For a short overview of the features with screenshots, it’d be best to visit our sneak peek announcement for RC1. Or check out a 4-minute screencast of the new interface in action. If you just want to jump straight to the good stuff here’s where you can find 2.5 upgrade and download information.
If you want to see everything I would grab a cup of coffee or a mojito, because this post is epic.