For ext3 to ext4 you can use:
tune2fs -O extents,uninit_bg,dir_index /dev/yourfilesystem
followed by:
fsck -pDf /dev/yourfilesystem
To return the system to a consistent state. However, I don't believe (someone correct me if I'm wrong) that this is a complete conversion. I believe there may be an issue with extents...
For FAT to NTFS:
convert (your drive letter here): /fs:ntfs
NTFS to XFS I have no idea but I would doubt it. NTFS is proprietary...