Some of the best kits to use are 1/35 or 1/24 model car kits. They usually have the entire engine modeled, with all parts moulded seperately, making for a huge range of different greebles.
They were used extensively on Star Wars models, and I recently used some parts from a 1/35 M3 Halftrack on a kitbashed/converted space station in 1/10000 scale.
Especially taking a part and using it in a vastly different scale takes all the associated context away, and the shape is disconnected from its origin.
Oh; I also used parts from a 1/700 (I believe?) battleship kit, which also worked great.
Long story short: just find a place that sells (old) model kits at discount prices, buy them, and have fun playing around with all the bits
