I have a directory on a network share called, oddly enough, Datasheets. Under datasheets I have folders for each vendor, as well as one for Specs (USB, PCI, etc).

Within each vendor's directory are subdirectories for part type, which of course varies with vendor. Under Analog Devices, say, I have opamp, adc, dac, reference, switch and the like. Under TI, I have usb, analog, logic, dsp, and under each of these are files or directories depending on how I want to organize. For example, in TI\USB I have a TAS1020B folder with the data sheet, related app notes and reference designs, etc. Under TI\analog, I have folders for opamp, dac, adc. Under each folder might be spice models, VHDL/Verilog models, IBIS models, JTAG BSDL files, etc ...

It sort of evolves as it grows, although sometimes it doesn't. I still have Cygnal and Burr-Brown folders which I oughta migrate ...

-a