Tips: Handy Linux Commands
This is by no means an exhaustive list, merely commands that I use on a daily basis that will be updated periodically as I can be bothered.
Use root complete with variables & script access:
sudo -
Renew DHCP lease:
dhclient -r
Restart networking:
/etc/init.d/network restart
Check CPU usage/processes:
top
Find commands:
apropos <command-or-pattern> man -k <command-or-pattern>
Find files & directories:
locate <pattern>
Display PCI devices:
lspci
Display USB devices:
lsusb
Display storage devices:
fdisk -l
Check for new hardware (Happens at boot time automatically):
kudzu --probe
Check for new hardware & test kudzu (requires rhpxl package):
ddcprobe
Gather information from the BIOS:
dmidecode biosdecode ownership #(Compaq specific) vpddecode #(IBM specific)
List drivers/kernel modules:
lsmod
Manually load a module and its dependencies:
modprobe <modulename>
Display information about a specific module or modules:
modinfo <packagename>
Launch the HAL device manager to examine all devices HAL knows about:
hal-device-manager
RBelTech 
Sudo isn’t enabled by default (well not for majority of accounts with RH though debian/ubuntu allow the access accounts to use it by default) and you can use Su – commands to do similarly the same thing. One thing I do like about sudo is the ability to log transactions (makes life a bit simiplier)