Dolphin GUI/Integrated Tools:
Memcard Manager: Fixed exporting gci files
Many fixes related to the GUI now supporting unicode
Move to wxAUI, which is wxw-speak for GUI with decently modern features :p
Gamelist has new, improved look and feel (you can jump to games alphabetically with you keyboard)
Added ability to dump full filesystems from GC and Wii discs. For GC discs, this includes the main apploader and dol

Dolphin Core:
Add "auto" mode to the frameskipper
_Massive_ stability fixes and bugfixes to JIT/JITIL
Implementation of Instruction Cache (interpreter only)
More accurate and complete FPU emulation (mostly visible in interpreter)
Added/Fixed Tool-Assisted-Speedrun features
Added the Triforce baseboard's SI and EXI devices (and JVS I/O), and media board behavior.

* Implementation is enough to get some games running, but requires more work for more games :)

Many fixes to Netplay feature
Allow plugins to be specified from the command line
Fix some issues with loading WADs
Stabilization of savestates
Added "Reset" function - the equivalent of tapping the reset button

Audio (Common audio features):
Added ALSA backend

Video (Common video features):
Fix PeekARGB
Fix flickering in some games
Optimization of shader generation and handling
Generally better shader error handling
Add widescreen hack

Wiimote (actually fixed in internal IPC HLE):
Fix wiimote usage in homebrew

Debugger:
Enable editing of registers displayed in the register window
Add ability to flip between ASCII and floating point values in mem view


OpenGL plugin:
Remove unneeded projection hacks

DirectX plugin:
Fixed up and FAST! (literally too many fixes for me to list ;p )
Enable toggling of safe texture cache
Enable toggling of EFB reads from cpu

Software Graphics plugin (NEW!):
Totally new plugin, intended for debugging and very accurate emulation - SLOW, don't feel the need to tell the team to make it faster :)

DSPLLE plugin:
More reversing done, more left to go :)

DSPHLE plugin:
Fix various games booting where they would hang before
Reversing and implementation of many of the more intricate behaviors of ucodes, expect better sound in most games.

DSPSpy:
Improve SD interaction
Fix rom dumping


Misc:
OSX build compiles and runs...(yes, even Snow Leopard)
OpenCL is being actively worked on to speed up texture conversion and other areas. Not enabled in normal builds yet.
Many, many tweaks here and there to increase speed, stability, and code cleanliness

I apologize in advance for leaving out specifics or possibly other notable changes, I tried to sum up 500+ revisions :p