'uname' will display various information about your system. Arch, kernel name, hostname etc.
'free -m' will display your RAM and Swap stats in MB
'uptime' will tell you how long your system has been running
'df -h' will tell you what filesystems are mounted, where they are mounted, and how much disk space is used on them
'fdisk -l' will show you your partition table
If you're looking for applets, there are programs like Conky
which will display system information.