Here are a couple I use at work a lot.

This one will identify the manufacturer of a NIC card based on the most current published list of OUIs. It takes the MAC address as the argument and is forgiving of the format (e.g. ifconfig, windows ipconfig, or cisco style)

#!/bin/bash

OUI=$(echo ${1//[:.-]/} | tr "[a-f]" "[A-F]" | egrep -o "^[0-9A-F]{6}")
lynx -dump standards.ieee.org/regauth/oui/oui.txt | grep $OUI

Here's one I use to mount the file system inside my Virtual Box .vdi disk image when I need to grab a file, but do not need to otherwise fireup the virtual machine:

#!/bin/bash

if [ -f ~/.VirtualBox/VDI/$1 ]
then
MOUNT=`sudo mount -o loop,umask=0000,offset=0x$(hd -n 1000000 ~/.VirtualBox/VDI/$1 | grep "eb 52 90 4e 54 46 53" | cut -c 1-8) ~/.VirtualBox/VDI/$1 /mnt 2>&1`
if [ "$?" -ne "0" ]
then
echo -e "Mount Failed!!!!\n"
OUT=`echo $MOUNT | grep "indicates unclean shutdown" 2>&1`
if [ "$?" -eq "0" ]
then
echo "NTFS was not cleanly unmounted"
fi
sudo losetup -d /dev/loop0
exit 0
fi
else
echo "$1 - files not found"
fi