Redistribute free space

Hi,

I have an external USB drive that has multiple partitions on it. I recently deleted a couple of those partitions but now there is empty space on the drive the cannot be claimed by any of the partitions. I realise Disk Utility is fairly limited in what it can do but is there a good third party app that will allow me to redistribute this empty space to the other partitions that are still on the drive? It is a fairly big drive with a lot of content so backing up, erasing and putting the content back on isn't really an option...

Thanks.