This is a list of commands that I use but always seem to forget:

List hardware information

These commands will require "sudo" privileges
  • biosdecode   Prints, to screen, information from BIOS memory about all of its known entry points.
  • dmidecode  Dumps the DMI or SMBIOS information, to screen, The Information in some cases could be unreliable as the  information contained in the DMI tables is sometimes inaccurate, incomplete or simply wrong.”
  • lshw
  • lshw-gtk  This is a GUI version of lshw above
  • hwinfo  

Mount a disk-image via loop-device

Assosiate a loop-device with a file
sudo losetup /dev/loopX <image file>

Find an unused loop-device
sudo losetup -f

Display all used loop-device
sudo losetup -a

Disassociate an existing loop-device
sudo losetup -d /dev/loopX

To mount the disk image, First identify the loop-device you would like to use.  Then associate it to the file name.  If you have an auto-mounter configure the device may be automatically mounted, otherwise you will have to manually mount it with the "mount" command using the loop-back device

You can usually perform the association and the mount in the one operation
mount -o loop <image file> <mount point>

Network Manager Appplet

For me, on Ubuntu 9.04 the Network manager applet dies every now and then.  Especially when editing/deleting wireless configurations.
To restart it do the following.
nohup nm-applet >/dev/null 2>&1 &

Youtube Audio

If you don't have audio in youtube the following will probably resolve it (on Ubuntu 8.04)
sudo apt-get install alsa-oss

Disk Recovery Tools

ddrescue in package gddrescue (the 'g' is for gnu, not gnome)

iPad/iPhone/iDevice - using Linux to get the UDID

To read the UDID in Linux just use:
lsusb -v 2> /dev/null | grep -e “Apple Inc” -A 2
This will print three lines per attached apple device: The manufacturer, the device name and the UDID (called “iSerial”).