Personally, if you're looking for a notebook that'll be useful and compatible with the modern world, I'd go for a PowerBook G3 or later. These machines can be had for under $200 nowadays, you can punt them across football fields with no major damage, and they can still run modern OSs and interface with modern hardware. A PoweerBook G3 will get you by, but if you want something that will be a decent little powerhouse with the ability to machine through the modern internet, you're going to want to go for a PowerBook G4. I would suggest either a late-model 12" G4 or the latest 15" you can afford. Avoid the Titanium PowerBooks these days, because they tend to run into issues relating to age and use. Personally, I'd go for the latest model 12" or 15" Aluminum PowerBook G4 you can afford. They're really wonderful notebooks, and still have more than enough oomph to get you through modern life.

Best of luck on your PowerBook hunt!