A Money class
Add a Money class to java.util that would encapsulate a currency and its value. Add the ability to also add a CurrencyConversionServiceProvider. This would greatly aid those of us that work with international currencies. As a standar part of the jdk it would put a stop to some of the (very) badly designed money implemations around ( or worse - people using floats/doubles for financial calculations ).
It would also help if the basic arithmetical operators for the class were overloaded. Writing long financial equations with BigDecimal is very unpleasant.