Partition Magic is now marketed by Symantec but was produced by PowerQuest and is a great piece of software. I have tried most of the parttioning tools and PM is the most effective and reliable I have found.
One word of caution though - PM hasn't been updated since 2002 (as far as I can tell Symantec haven't put out a single update since they acquired it) and drive specs have changed since then. I am not sure how it will handle the very large capacities of some modern drives, and I am not sure about its support for SATA drives. One of the things Powerquest used to do was issue updates to support new drive capacities, drive formats, bug fixes and new drive interfaces.
One of the other things PM is excellent for is upgrading hard discs as it will copy partitions from one drive to another and resize them as you want on the new drive.
The other popular partition manager I have a copy of is Acronis Disc Director, this has the advantage that it is still being actively developed however the software is Linux based and you may find some oddities in the way it handles your drives, especially if you need to run the recovery software from CDROM. I can't get the CDROM to recognise my RAID array at all, whereas PM handles it with ease from a floppy disc!