$ dmesg => Detected hardware and boot messages (dmesg many more options)
$ cat /proc/cpuinfo => CPU model
$ cat /proc/meminfo => Hardware memory
$ cat /proc/interrupts => Lists the number of interrupts per CPU per I/O device
$ lshw => Displays information on hardware configuration of the system
$ lsblk => Displays block device related information in Linux (sudo yum install util-linux-ng)
$ free -m => Used and free memory (-m for MB) (free command in detail)
$ lspci -tv => Show PCI devices (very useful to find vendor ids)
$ lsusb -tv => Show USB devices (read more lsusb options)
$ lshal => Show a list of all devices with their properties
$ dmidecode => Show hardware info from the BIOS (vendor details)
$ hdparm -i /dev/sda # Show info about disk sda
$ hdparm -tT /dev/sda # Do a read speed test on disk sda
$ badblocks -s /dev/sda # Test for unreadable blocks on disk sda
$ lsblk -o NAME,FSTYPE,UUID,RO,RM,SIZE,STATE,OWNER,GROUP,MODE,TYPE,MOUNTPOINT,LABEL,MODEL # list all block devices like harddrives or usb drives