lspci ( lists pci device)
lsusb ( lists usb device)
lsscsi ( lists scsi device)
systool
fdisk -l ( lists hard drive)
dmidecode ( lists hardware model, serial number, cpu, memory. This command was handy when i needed to find serial number without a visit to data center)
cat /proc/cpuinfo ( more on cpu)
cat /proc/meminfo ( more on memory)

you can find a lot of information by using dmesg|more or grep what you are looking
e.g.
dmesg | egrep ‘(SCSI|scsi0|ide0|hda|sda|serio|mice|eth0|eth1)’

cat /proc/cpuinfo

cat /proc/meminfo