In fact, XFS is almost nothing like EXT3, aside from the fact that it does journaling, and is a file system. XFS stores unallocated blocks in spanning b-trees, as opposed to the primitive bitmaps used by ext3. Also, the file system structure of XFS was designed for journaling, unlike the hacked-together mess that is EXT3. Not to mention that XFS is highly paralized, highly threaded, and very good at streaming off multi-terrabyte files. It's one shortcoming is that it makes fairly inefficient use of disk space. This is balanced out for it's ability to work on 512 peta-byte drives.

You might also want to check out JFS.

XFS information can be found at http://oss.sgi.com/projects/xfs/.