Blender 2.68 Final + Portable

Modeling
Improved bridge tool to bridge multiple loops at once, subdivision, surface blending and bridging face regions. New grid-fill tool filling a grid from edge loops, X mirror and projected proportional editing, snap to symmetry, face split option for dissolve, vertex connect cut across faces.

Physics
Smoke has improved rendering quality avoid blockiness, and subframe simulation support to handle fast moving emitters. Particles can now be emitted from faces generated by modifiers that were not in the original mesh.

Cycles Render
Rendering performance has been improved on CPU and GPU and support for new GPUs was added. A new Mist render pass is available, Ray visibility is now supported for all light sources, and new Nodes have been added. Hair rendering on the GPU has been enabled as well.

Motion Tracker
Some new features and smaller improvements to existing ones were done for motion tracking. Main features are markers' position refining, which allows you to refine marker position after it was occluded by an object, and automatic keyframe selection, which tries to automatically find a best keyframe for the reconstruction.

Usability
Improved weight painting tools, mask modifier for sequencer strips, 2D image paint more consistent with 3D painting, better key shortcuts display, quick enabling and disabling of multiple layers or visibility, auto indent for multi-line Python statements,

Python Security
Auto-running Python scripts can now be controlled more securely.

Addons
New addons are Texture Atlas to bake shadow and lightmaps for an entire scene, and Edit Linked Library, for quick editing of linked assets.

Bug fixes
In addition to the new features, over 280 bugs that existed in previous releases have been fixed.