From Coriolis Systems:
iPartition is a disk partitioning utility for Mac OS X with the ability to resize Mac OS extended (HFS ) partitions and Windows partitions while keeping their contents intact. Additionally, iPartition's intuitive, easy-to-use interface and built-in intelligence that saves you from having to reorganise your disk by hand to make contiguous space makes iPartition perhaps the easiest partitioning tool ever released. Whether you want to partition your disk to try Linux, test the latest version of Mac OS X, optimise the performance of enterprise database applications, set-up an external disk capable of booting both Intel and PowerPC Macs, or simply restrict disk space usage by temporary files and swapfiles, iPartition can help you. In version 3, you can now resize Windows partitions which means you can adjust the size of your Boot Camp partition.