uname -a - returns the OS level backwards
e.g. AIX 5.1 
# uname -a
AIX orgo 1 5 000C736D4C00

to get the system patch level:
# oslevel -r
5100-07

list software products (packages)
# lslpp -L

display the error report
# errpt -a

display the devices
# lsdev -C

display the disks
# lsdev -Cc disk

display the physical volumes
# lspv

display attribute characteristics and possible values of attributes for devices
in the system.
# lsattr -El sys0


display user account attributes
# lsuser

----- other commands -----
odmget
instfix
mksysb - creates an installable image of the root volume group either in a file or onto a bootable tape
chfs - change attributes of filesystem
crfs - add a filesystem to a logical volume within a previously create volume group
mkfs - make file system
mklv - create a logical volume
chlv
extendlv
mklvcopy
rmlvcopy
syncvg
lslv
chpv - change physical volume
lchangepv
ldeletepv
linstallpv
lquerypv
lresyncpv
lspv
migratepv
replacepv

installp - installs available software products in a compatible installation package
mkinstallp - make installp packages