So, the Summer of Code 2008 projects were posted a few days ago.
A few of the ones I think are particularly interesting:
PHP: Zend LLVM Extension
Vim: On-the-fly Code Checker, Visual Studio 2005/2008 Plugin
Python: Django on the JVM
Mercurial: Rebasing, svn tools, partial cloning, TortoiseHG for Linux
LLVM: C++ classes support, llvm/clang distcc, STM support
GCC: Windows Improvements, C++0x lambda functions
Boost: Multi-core/SIMD optimizations for Boost::Math and Boost::Graph
Cairo: HDR image surface type
Portland State University: A System for Patent Categorization and Analysis,
X.Org: GPU-Accelerated Video Decoding
Other thoughts: Gosh, Python and KDE have a lot of projects! Looks like Cython and NumPy are popular Python subprojects. Mercurial is four for four in terms of interesting-to-me projects. Five of eight Linux projects are printing-related.
Good luck to everyone working on it this year!