Extending root FS on LVM

With e2fsprogs this works online for ext3 and ext4 on fedora 8 and 11:

pvresize /dev/sda3
lvdisplay
lvextend /dev/VolGroup00/LogVol00 -L +2G
resize2fs /dev/mapper/VolGroup00-LogVol00

If you like GUI, use system-config-lvm.
If your linux runs under vmware, extend vmware disk as:

vmware-vdiskmanager.exe -x 10GB disk.vmdk

For details refer to vmware disk section.