I'm using the System Monitor panel applet to show me graphs of current ram usage and network traffic. However, I want something like iStat Menu's text version of this.
If I hover over my current app, it shows that instant's traffic, but does not update.
Is there something that will display a number (not graph) of real-time network traffic?
At least for network traffic, you can use GNOME Netspeed Applet
I couldn't find anything for memory usage to be reported in this manner on gnome-panel, though it seems like it should be an option of the default system-monitor applet.
You can use Conky, it's a lightweight system monitor, and highly configurable. You can choose from a wide list of parameters to display, not only network data, but memory, processor, etc. However information is displayed on your desktop background, so I'm not entirely sure it fits your needs.
Have a look at Conky – a light weight system monitor for Ubuntu Linux Systems, it has some screenshots and directions on installing it on Ubuntu (via repositories). The configuration is easy, but is made through text files, so you have to be prepared to fire up your favorite editor.