fuse-ext2 works but is very slow (I get some 7 MB/s reading and 1 MB/s writing via USB 2.0).
If you have the choice, better use Apple's HFS+ on the external drive, which is much faster
(I get some 30 MB/s both reading and writing, both on Mac and Linux).
HFS+ is supported by Linux mostly out-of-the-box. To get write access even to a journaled partition on Ubuntu, install support via
sudo apt-get install hfsprogs and when the drive is mounted (e.g., automatically), re-mount it writable using
sudo mount -o remount,force,rw /mount/point
BTW, recently I suffered from a Mac OS crash apparently due to fuse-ext2