The Indivision Scandoubler/Flicker Fixer also known as a Toastscan in the US/Canada is a good choice the only problem I have with it is it takes about one minute before it sysnc's up properly and the image stops flikering on the PC monitor I am using.
You can also go with a used internal graphics card (Picasso, Cybervision, GVP and others) but this will usualy cost more.
