You guys know the drill! :)
* MiniUsage – 1.5.0 (Free) Leopard – 10.5 – http://nsek.net/SYW/software/english/miniusage/index.html - What to say about an app that says almost everything that is happening on your computer right now… CPU usage, amount of network flow, battery status and process namesd etc. It takes very little space and is a perfect fit for iBooks/PowerBooks. While the application is running, this information can be referred via AppleScript. Now you can see just what is slowing your computer down!
* MenuMeters – 1.6 (Free) Tiger/Leopard – 10.4 or 10.5 - http://www.ragingmenace.com/software/menumeters/index.html – MenuMeters is a set of CPU, memory, disk, and network monitoring tools for Mac OS X. Although there are numerous other programs which do the same thing, none had quite the feature set I was looking for. Most were windows that sat in a corner or on the desktop, which are inevitably obscured by document windows on my laptop’s small screen. Those monitors which used the menubar mostly used the NSStatusItem API, which has the annoying tendency to totally reorder my menubar on every login.
The MenuMeters monitors are true SystemUIServer plugins (also known as Menu Extras). This means they can be reordered using command-drag and remember their positions in the menubar across logins and restarts.
* iStat Menu – 3.19 (Shareware) Leopard – 10.5 – http://bjango.com/mac/istatmenus/ You can download here: http://istat-menus.mac.informer.com/3.19/ – It display the usage on your menubar but you can add or remove items straight from System Preferences. This is the last version available for 10.5 PowerPC. I was able to download (version 2.0) from this link, and here you also will be able to download an option for Tiger 10.4 (version 1) – http://istat-menus.en.softonic.com/mac/download-version/istat-menus-3.20