Ram Meter is a utility for Windows 7 which will display the Ram Usage on the taskbar (Actually it displays under the taskbar, so you need to enable the transparency of the Taskbar).
Features
Colour changer - Normal, warning and critical colours
Warning and critical percentage changer
Left to right or right to left
Uses only 9 MB of memory itself!
System tray icon
Start on Windows Login
Hidden from ALT-TAB list
Not working things:
Multi-display (It works on the Primary display)
Resists show desktop (Show desktop will hide this application too)
Left and right positioned taskbars
Read more and Download the Simple RAM meter
[Via The Windows Club]