Like Scott (thefyingcamera) I do like Exacta's, they are fun to use and there's plenty about still in good working order. and you can build up a good system for not too big an outlay. There's a wide array of lenses from a variety of manufacturers for them as well.
More collectible are the lesser known Praktina's made by KW and originally designed while under the ownership of Charles Noble a German born American. (Quite an interesting story in itself worth looking up). Under communist control the company was merged with Zeiss Contax to form Praktica, and they intern later absorbed Exacta,
The Praktina was the first full 35mm SLR system to have a motor drive, you sometimes see system parts selling for high prices to collectors at camera fairs.
Ian