I have bought a few different packs from shapeways. Always in the cheapest, Frosted Ultra plastic. All the ones I have are from Giles's Design (formerly known as aegidian), who has several of the appropriate scale.
I have a set of the 1971 Le Mans cars that I've finished painting as well. They're just a slight bit too large in length for most spaces on the track, but the width is fine and the size doesn't detract. I will take a picture and post it.
I've also got the 1957 and 1962 Formula 1 sets, which I applying the final details to. I found these to be the most challenging to paint because of the larger, open cockpits. The 1962 set are particularly small what with the skinny chassis and wide set wheels. I'll post pictures when they're done.