dmidecode is a tool for dumping a computer’s DMI (some say SMBIOS) table contents in a human-readable format. Generally this will include all the important hardware in the computer.

lspci is a utility for displaying information about all PCI buses in the system and all devices connected to them. In particular, lspci -vvv can be very useful displaying information about many hardware items in the computer.

Some other basic commands that provide information on the hardware Linux is running on.

ifconfig -a
List the network interfaces including any that are currently down. Provides the IP and MAC addresses.
route -n
Shows the gateway being used and other network device information.
cat /etc/resolv.conf
Shows the DNS that are used to resolve names and any domains that are searched.
cat /proc/cpuinfo
Detailed cpu information including type, speed and number of cores.
Shows all the devices plugged into the PCI bus. Typically this provides the display controller, network card, sound card and other periferals.
cat /proc/interrupts
List all interrupts. Look for conflicts or sharing between devices.
fdisk -l /dev/?d?
List disks being used with type.
cat /proc/ide/hda/model
Display disk device model.
cat /proc/filesystems
List supported file system types.
List USB devices currently plugged in.
dpkg -l
On a Debian based system (e.g., Ubuntu), list installed software packages.
List full hardware in the system. Requires root authority for all the details.