Native libgmp for faster number crunching
Maybe someone should incorporate the native libgmp library into OpenJDK.
See the recent threads titled "Removed GMP math?" in the Kaffe and Classpath mailing lists for some details.
You might get the impression that libgmp might only help in extreme corner cases where you have really huge numbers, but I've found that Java is several times slower than C/C++ even on a reasonable benchmark that deals with not-so-huge numbers.
If you act quickly to get in a proposal to the OpenJDK Challenge, you could get paid to do the work.