How can I quickly build PCB prototypes?
For fairly simple design and medium trace width you can either draw the traces on the raw PCB board with an etch-resistant paint and etch the rest of the cooper out by some chemicals, such as Iron Chloride (FeCl3) or Cooper Sulfate (CuSO4). For better quality you can print the layout of the traces on a transparency and use the photo-developing process to develop the design before etching. 

For example, here is a nice Makezine article about how to make DIY PCBs
http://makezine.com/projects/cheap-friendly-and-precise-pcb-etching/

However, for designs with multiple layers, tiny SMD components, BGAs, High speed digital signals, with silk screen and solder masks, and traces under 10mils you'ļl be better off ordering a PCB from one of many PCB fab houses. Some offer expedited services - PCB in a couple days, if you can afford the cost and shipping.