Best File System for Cross-Platform backup

[Amit Uttamchandani <amit.uttam@gmail.com>]

I got an external hard drive to do some backup and it was formatted as
FAT32, which is a logical choice. But I thought why should I use FAT32.
I have a Debian Testing and a Mac Machine. I could use a more advanced
file system that has journalling, etc.

So I decided to do a compromise. I formatted 100GB as Fat32 in case I
need to plug it in to a windows machine. But the rest is in ext3
format. So I used gparted to do this. But now when I mount the ext3
partition, only root can copy files to it. Why is that?

Also, what other file systems should I use?

Thanks,
Amit