You can also use easier to find PC133 RAM.
(link)
Remember that all cubes by now are 5-6 years old
(link) and that harddrives, cd-rom etc may soon die. The original ATI Rage Pro (16MB) is a bit on the weak side for OSX's visual effects - expect som lagging when using exposé, scrolling etc.
I would consider the G4 cube more as a collector's item than a machine to be used daily for several more years with gradually updated softwares and OS - unless you upgrade the GPU and CPU. And its looks will come to a shame next to a Dell monitor
Apart from the recommended Mac mini above, a used iBook G4 (800MHz-1,33 GHz) is also a good choice. The later models all have wifi built in and are generally trouble-free. They are also small and easy to stow away if you are not using the computer all day and do not feel like having a desk crowded with cables, monitor, keyboard etc. (The cube is beautiful and small but requires a lot of ugly cables...).
That said, the G4 Cube is in no way a bad machine. I use a PM G4 (350 MHz Yikles! which is quite close to the cube in specs) as well as a iBook 1,2 GHz and both are very useful machines. But the PM is starting to show it age when it comes to graphics and general responsiveness compared to even a lowly iBook...
Never go below 512 MB RAM. At least 768 MB or more is preferred.